Of course the camera is yours to alter as you please but Pls dont make a frankenleica!
Personally, since switching to MP, i find myself itching for the M6/M4 lever. This is because that extra piece of swivelling plastic i got this habit of twiddling with my thumb when on the hunt for a subject. I find the classic lever on my MP quite bland coz it lacks the extra hinge where the plastic is. So there isnt an extra piece to twiddle. Quite phallic really.
Back to your topic, i remember seeing frankenleicas with changed levers before. It should be possible but its a big job and the whole top must be removed. would suggest you consult leica technician like master tay. I assume you are not doing yourself.