You can indeed.
I have this in my .vimrc
; it swaps :
with ;
, which means that I can activate command line mode with a single keystroke:
nnoremap ; :
nnoremap : ;
You could of course substitute any key you like (and that you don’t mind remapping — if it’s already assigned to a command, ideally it’s not to a command that you use very often) for ;
.