I haven't had my M&P40C apart lately, but from memory the magazine disconnect is the same as the "disassembly lever" (that yellow thing), except for some spring loading to force it into the "disconnect" position if the magazine is removed. The disassembly lever doesn't have that spring.

Adding (or removing) that would be trivial, and applies to all of the non-Shield versions (I'm not 100% on the .45 version, but it should be the same).

However, the thumb safety is another animal. The Hilary Lock is not present on/in the sear assembly, and the space where the Lock's hole would be is covered up by some small parts and a spring that do the necessary blocking.

This requires (besides the cutout in the plastic grip) the proper sear assembly, a little spring, and a tiny cam. (And the safety lever.) There's just no place to put these parts in the non-thumb-safety assembly except for cutting the grip for the lever.

(IMHO, the thumb safety may have been an afterthought at S&W. I think that the magazine safety, bearing in mind that Hilary Locks popped into S&W's line for a while back then, came into being when somebody noticed the simplicity of adding it with just a couple of parts.)

I'm neutral on the magazine disconnect. I don't believe that, in extremis, you'd manage to drop a magazine.... But, unless you're married to hot magazine changes (useable round in chamber), I don't see much hurt. YMMV....

The thumb safety, OTOH, just seems to be "right" only in the sense that it operates in the "standard" fashion - "down", rather than "up". I have a couple of older S&W semi's that I don't carry for that reason. Just too easy to move.... (The Shield's thumb safety is closer to reality, although, IMHO, the lever's a tiny bit too small. 1911 folks are at least used to the direction. It's also trivial to remove.)

Unfortunately, it's still (IMHO) a bad idea to remove a manufacturer-supplied safety device....

Regards,

__________________
Stu.