You could hurt the car if you go crazy with the tune, Mo's and Lidio do their tunes safely for the average Joe.
The transmission reschedule is worth the tune alone. No more 4th gear at 30mph. Car will hold the right gear til it needs to shift.
I also believe the timing can be played with and Mos' and Lidio do that.
We've been running an aftermarket tune for along time with no issues other than state inspection. All you need to do is put the OEM tune back in, zip though inspection then put the performance tune back in and your car is driveable again.
Lidio at Alternative Auto has a tune for the MM as well as Mo's. Been some reports he's not doing them anymore, but I'm not sure about that. We have one of each and they are both great.
If you don't have a Mo's tune or one from Lidio, get one. Everyone here will tell you it's the #1 mod to do, followed by boost in which you will need tune for as well.