Minimizing the cut depth as SD mentions will also minimize splintering.
In this case, I'd be real tempted to try to create a new lift-out in the area where it's needed.
Failing that, if you're determined to cut across the sole, and you don't have the tools or skills, most stores like Home Depot will do cuts, but you'd be better off taking it to a cabinet maker, they'll care more about the results.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"