Basically, you are only working on the non-special characters, so a simple "replace" may suffice:
replace $1- a,s; s, d; d,f ; f, g; g, h; h, j; j,k; k,l; l,a
etc.
Don't have mIRC running at the moment, so I can't check on the syntax of replace/replace cs.
Cheers,
DK