diff --git a/hosts/yarn/default.nix b/hosts/yarn/default.nix
index bd71dca..abc5fa6 100644
--- a/hosts/yarn/default.nix
+++ b/hosts/yarn/default.nix
@@ -87,11 +87,17 @@
   # The module discovers FH5's install path from Steam's library metadata
   # and replaces the BK2 file with a 0-byte stub. Re-applies daily via
   # systemd timer so Steam verify/updates don't silently undo it.
+  #
+  # Two copies live in the install: media/UI/Videos/T10_MS_Combined.bk2
+  # (SD) and .../hires/T10_MS_Combined.bk2 (hires). The engine picks one
+  # based on the installed asset profile, so we stub both for guaranteed
+  # coverage. PCGamingWiki documents both paths under "Skip intro video".
   services.gameMods = {
     enable = true;
     mods."fh5-no-intro" = {
       steamAppId = 1551360;
       files."media/UI/Videos/T10_MS_Combined.bk2".empty = true;
+      files."media/UI/Videos/hires/T10_MS_Combined.bk2".empty = true;
     };
   };
 }
diff --git a/modules/desktop-game-mods.nix b/modules/desktop-game-mods.nix
index c4ec272..8da04fd 100644
--- a/modules/desktop-game-mods.nix
+++ b/modules/desktop-game-mods.nix
@@ -6,18 +6,27 @@
 }:
 # Declarative game file mods. Define per-game file replacements keyed by
 # Steam App ID. The module produces a `game-mods-apply` script that
-# discovers the game install directory from Steam's own library metadata
-# (so it survives drive moves and library reconfigurations) and applies
-# the specified file operations.
+# discovers the game install directory (and Proton prefix) from Steam's
+# own library metadata, so it survives drive moves and library
+# reconfigurations.
 #
 # A systemd timer re-applies mods daily so Steam verify/update restores
 # don't silently undo them.
 #
-# Example:
-#   services.gameMods.mods."fh5-no-intro" = {
+# Each file op picks two axes:
+#   mode      = "replace" (default, skip if absent) | "create" (mkdir + write)
+#   location  = "install" (default, steamapps/common/<dir>) | "prefix"
+#                (steamapps/compatdata/<appid>/pfx — for user-storage mods)
+#
+# Example: stub the cold-start intro video, plus drop a sound mod XML into
+# the Wine prefix's user storage.
+#   services.gameMods.mods."fh5" = {
 #     steamAppId = 1551360;
-#     files."media/UI/Videos/T10_MS_Combined.bk2" = {
-#       empty = true;
+#     files."media/UI/Videos/T10_MS_Combined.bk2".empty = true;
+#     files."drive_c/users/steamuser/AppData/Local/ForzaHorizon5/User_SteamLocalStorageDirectory/ConnectedStorage/ForzaUserConfigSelections/mods/audio/foo.xml" = {
+#       source = ./files/foo.xml;
+#       location = "prefix";
+#       mode = "create";
 #     };
 #   };
 let
@@ -42,6 +51,36 @@ let
         default = null;
         description = "Replace the file with contents from this store path.";
       };
+      mode = mkOption {
+        type = types.enum [
+          "replace"
+          "create"
+        ];
+        default = "replace";
+        description = ''
+          How to handle a missing target.
+
+          - `replace` (default): only act when the target already exists; otherwise skip.
+            A backup is written next to the target on first apply.
+          - `create`: create the target (and parent directories) if absent; replace it
+            otherwise. No backup is written when the target did not exist.
+        '';
+      };
+      location = mkOption {
+        type = types.enum [
+          "install"
+          "prefix"
+        ];
+        default = "install";
+        description = ''
+          Root the relative target path is resolved against.
+
+          - `install` (default): the Steam install directory (`steamapps/common/<dir>`).
+          - `prefix`: the Proton/Wine prefix root (`steamapps/compatdata/<appid>/pfx`).
+            Use this for mods that write into the game's user storage under
+            `drive_c/users/steamuser/AppData/...`.
+        '';
+      };
     };
   };
 
@@ -59,32 +98,29 @@ let
     };
   };
 
-  # Store each replacement file in the Nix store.
-  gameModFiles = lib.mapAttrs (
-    _: mod:
-    lib.mapAttrs (
-      relPath: op:
-      if op.empty then
-        pkgs.runCommand "game-mod-empty" { } "touch $out"
-      else if op.source != null then
-        op.source
-      else
-        throw "game-mod file '${relPath}': set empty = true or provide a source"
-    ) mod.files
-  ) cfg.mods;
+  # Resolve the on-disk source for a single file op (empty stub or user-provided path).
+  resolveSource =
+    relPath: op:
+    if op.empty then
+      pkgs.runCommand "game-mod-empty" { } "touch $out"
+    else if op.source != null then
+      op.source
+    else
+      throw "game-mod file '${relPath}': set empty = true or provide a source";
 
-  # Generate mod data as JSON for the apply script.  Each entry is
-  # { appId, target (relative), source (Nix store path) }.
+  # Generate mod data as JSON for the apply script. Each entry is
+  # { steamAppId, target, source, mode, location }.
   modData =
     let
       entries = lib.concatLists (
         lib.mapAttrsToList (
-          modName: mod:
-          lib.mapAttrsToList (relPath: source: {
+          _modName: mod:
+          lib.mapAttrsToList (relPath: op: {
             inherit (mod) steamAppId;
             target = relPath;
-            inherit source;
-          }) (gameModFiles.${modName} or { })
+            source = resolveSource relPath op;
+            inherit (op) mode location;
+          }) mod.files
         ) cfg.mods
       );
     in
@@ -155,42 +191,69 @@ let
             return None
 
 
-        def apply_mod(appid, target_rel, source):
-            game_root = find_game_root(appid)
-            if game_root is None:
+        def find_compatdata_pfx(appid):
+            """Return the Proton/Wine prefix root for `appid`, or None if not found."""
+            steam_root = find_steam_root()
+            for lib_path in find_libraries(steam_root):
+                pfx = os.path.join(
+                    lib_path, "steamapps", "compatdata", str(appid), "pfx"
+                )
+                if os.path.isdir(pfx):
+                    return pfx
+            return None
+
+
+        def find_root(appid, location):
+            """Resolve the directory `location`-relative paths apply under."""
+            if location == "install":
+                return find_game_root(appid)
+            if location == "prefix":
+                return find_compatdata_pfx(appid)
+            raise ValueError(f"unknown location {location!r}")
+
+
+        def apply_mod(appid, target_rel, source, mode, location):
+            root = find_root(appid, location)
+            if root is None:
                 print(
-                    f"game-mods: Steam app {appid} not found"
-                    " in any library, skipping",
+                    f"game-mods: {location} root for app {appid}"
+                    " not found, skipping",
                     file=sys.stderr,
                 )
                 return
 
-            target = os.path.join(game_root, target_rel)
-            if not os.path.exists(target):
+            target = os.path.join(root, target_rel)
+            target_existed = os.path.exists(target)
+
+            if not target_existed and mode != "create":
                 print(
-                    f"game-mods: target '{target}'"
-                    " does not exist, skipping",
+                    f"game-mods: target '{target}' does not exist"
+                    f" (mode={mode}), skipping",
                     file=sys.stderr,
                 )
                 return
 
             # Already applied?
-            if os.path.isfile(target) and os.path.isfile(source):
+            if target_existed and os.path.isfile(target) and os.path.isfile(source):
                 with open(target, "rb") as ft, open(source, "rb") as fs:
                     if ft.read() == fs.read():
                         return
 
-            # Back up the original (once).
+            # Back up the original (once), if it existed.
             backup = target + BACKUP_SUFFIX
-            if not os.path.exists(backup):
+            if target_existed and not os.path.exists(backup):
                 shutil.copy2(target, backup)
                 print(
                     f"game-mods: backed up {target} -> {backup}",
                     file=sys.stderr,
                 )
 
+            if not target_existed:
+                os.makedirs(os.path.dirname(target), exist_ok=True)
+
             shutil.copy2(source, target)
-            print(f"game-mods: replaced {target}", file=sys.stderr)
+            verb = "created" if not target_existed else "replaced"
+            print(f"game-mods: {verb} {target}", file=sys.stderr)
 
 
         def main():
@@ -203,6 +266,8 @@ let
                     str(entry["steamAppId"]),
                     entry["target"],
                     entry["source"],
+                    entry["mode"],
+                    entry["location"],
                 )
 
             print("game-mods: done", file=sys.stderr)