There are a lot of things you CAN do but not all of them make sense.
I would (DID!) buy the M&P9. No thumb safety, no magazine disconnector.
Burwell trigger job and fibre optic front sight.
It suits me well in IDPA SSP and would be fine in USPSA Production.
A .40 would let you shoot USPSA Limited-10.
A .45 would let you shoot IDPA CDP.
But those are kind of a stretch for the model unless you are so good that the gun makes little difference.
Look at the M&P Pro 9 or 9L. A little extra sight radius usually helps.