It would be nice to do it in game but it still wouldn't be as robust as Steam's custom controller profiles so I probably wouldn't use it anyway. Speaking of which you shouldn't have to use big picture mode to use custom controller option. I thought I had to initially as well because Steam kind of tries to make you think that. Open Steam and go click For Honor in your library opening its page. In the categories at top, the far right option is Controller Configuration which gives the same options as big picture. Also if using a DS4 controller do not run DS4Windows.exe when playing for Honor and restart if it had been previously run. Not needed anymore and causes conflicts.
Also I can share you my For Honor controller set up if you want to try it. Also I am interested in which key binds you would like to alter as I am always tinkering with it and trying new things to find best set up. Sometimes it depends on the hero but I am always willing to hear ideas. Anyway hope it works for you because big picture mode really does suck.
Thanks for the reply Xavyn. I'm using the DS5 and since it doesn't have a lot of support yet so it requires big picture to function. The problem is when Big Picture is in use the game doesn't function properly. I still get Xbox buttons even though I set the in game options to Ps4 and the controller remapping doesn't appear in game.
I've played this game since beta and I've always had my set up as just switching the sprint and the guard break button Left thumbstick click and square). I can do that in Big picture, but for some reason it also doesn't let me hold in the left thumbstick to do my 4th execution since Big Picture only has execution 1 and 2 as inputs.