I cannot find where 'custom' key mappings are kept. They don't seem to be in any of the ini files, or at least that I can see. I see mention of a controlmap.txt file, and another mention of some customcontrol something somewhere in \common\skyrim\data\ something... None of which seem to exist. Yet, my keys stay remapped, so where are they read from?

The file is ControlMap_Custom.txt located in the Skyrim folder.

It's a binary file, so it can't be edited.

..But can it be copied into a new instance of Skyrim and be recognized? Or does there have to be some other event (like remapping the keys) that tells TESV that the file exists? It doesn't exist if you have not remapped your keys, BTW.

Try it, move the file over, launch the game. It will either work or not. If it does not, remove the file, remap a key, then swap the created file with the old install one, try the game again. If that does not work, then put back the game created file and remap the keys in game.

Wish notepad++ would do binary... renamed the controlmap to .bak, no mapped keys. renamed it back to .txt, remapped keys. So, to answer my own question, yes - I could just copy over a cotrolmap_custom.txt file from an old instance to a new instance of skyrim. Won't fix the naming issues in the menus, but will avoid issues when one stupidly re-maps the [enter] key. (This makes it almost impossible to undo that wee mistake...) Or, one could just delete the file, then re-create it in-game...