i can respect that, i like consistency myself...
as far as i'm aware though, there shouldn't be a discernible difference between firmware 4.0.1 and 4.1 in terms of loading games and homebrew, unless there is a game out there that requires resources from 4.1 that don't exist in 4.0.1, then i'm just talking out my ass here.
you can go ahead and proceed to do what you planned with your brother's switch, installing 4.1 with autoRCM onto it, but i WOULD also recommend keeping a backup of 4.0.1 before doing that just to keep a clean copy of the 4.0.1 firmware should you ever need to return to it, for example if your brother has connected to the internet with that firmware, then you'll need to restore that same clean dump to mitigate a ban. you'll also be able to boot the 4.0.1 firmware on his switch without having to worry about bypassing the fuse check.
Thanks the the advice buddy. I'll make sure I get a nand backup of 4.0.1 before I do anything. I can do this via hekate before installing custom firmware right?