Below, in quotes, are instructions I got this from an earlier thread about this but I thought I'd post it here to help you all out. Sorry I can't give credit to original poster because I didn't copy that part.
I did this process, and though very time consuming, it does work. Be VERY careful the order you Edit/Replace keys. Whatever your new destination key is MAKE SURE it's NOT ASSIGNED TO ANYTHING ELSE. If you move W to E you have to move what was on E first or else they're ALL assigned to E and you have to go through one by one to change those out to the right key. Like the OP below, I HIGHLY, HIGHLY, HIGHLY recommend NOTEPAD ++. Made life much easier and it's free. I also definitely made back ups in a completely different folder before I started.
Couple notes that happened to me:
- I couldn't get Grenades/Quick Access to work on anything but Middle Mouse Button.
- Don't remap Call Horse (X). There's a bug. Talked about in another forum.
- Strong attack CAN be mapped to a single button. I have it on R and have no problems.
- Couldn't map to any symbol buttons, [, \, ;, etc.
"C:\Users\*your window session name*\Documents\The Witcher 3 and opening "input.settings" ( i strongly recommand notepad ++ ) will allow anyone to fully rebind ALL keys.
For exemple if you want to rebind w a s d,
1- use the "replace" function from notepad++ and search for IK_W= ( for exemple )
Its important to ALWAYS keep the "=" in the search / replace ( just in case the "W" would just be the first letter of a word.
2- Then in the "replace by" type IK_*the letter you want use"= ( always keep the "=" )
3- Select "replace all"
Do that for all keys you want to replace
Because in this file the default "IK_W=" is listed several time for differents action like : geralt movement / horse movement / boat movement.. Its like that for every function, like the "use" is listed for like 40-50time differents actions
You can do that following the same method for anything you want. And to easlyly find the function you want, open the game go to the key configuration, check the key and do a search in the file with notepad++
Its a bit tricky, and take a little time but you are going to be able to remap ALL keys ( even the locked one in the menu, like character / inventory.. etc ) without any issues.
Would have been better to have a proper rebind ability from the beginning, but still better than having to play with the default keys or bothering with a autokey or whatever other software"