I recommend AutoHotkey
. It's a scripting language, so it might seem daunting at first if you've never done any programming before, but it's really easy to remap keys for a specific program. Here's an example similar to what I used to remap the save and load state keys to where I'd normally have them in emulators:
In English: if the active window title includes the letters "FBA" or "FinalBurn" (because I don't remember which actually goes in the title) then pressing the semicolon or q keys will cause AHK to tell the app that you pressed f5 or f7, respectively, instead of the original keys.
PS. I'm off the project. I haven't had much time or motivation for anything TAS-related this year, and moreover no longer have a Windows box to build on. Apologies to anyone I've let down. :(