A tuner won't break the transmission.
If you drive it right and don't overload it the tuner can't do anything. If it's not right and you keep driving it it will break and that's your fault. If it's stock and you drive it like that it will break and it's your fault again.
Everybody pays for the thieves that are unable to be honest and pay up. Why not just go in and rob somebody to get the money to fix it?