As noted,, I do not think a 38-40 cylinder can be reamed to accept 10mm.
Another note.
If you have one of the rarer variations of Ruger that accepts 38-40 or 40 S&W and desired to shoot 10mm, a spare cylinder would be the best way to accomplish this. Find a .357 cylinder, that fits, and have it properly reamed to accept 10mm. That way, you could keep the rare variation intact, and still be able to enjoy a different caliber.