How do you want to change it from a standard TKL? Do you want multiple programmable layers, different layout etc?
It sounds to me like you might be better off going for a non-gamer board, like a Ducky, Filco, Varmillo or whatever, and maybe customising the keycaps and using software like autohotkey for anything else you want. Get a switch tester or try different switch types if you can, switches are very much personal preference, as are caps. You will need stabilisers for any large caps, like enter and space. There are two common types, cherry, and costar. Cherry, like extra mini switch posts, are easier to swap caps with, but costar, the wire type, are often preferred for feel and occasionally sound.
