In repairing the horn, both windows, radio.

In repairing the horn, both windows, radio, clock on my son's 2001 V6 base Camaro, the mechanic told me that the computer and engine management system analysis showed that his car required a BCM computer module. After installation of the BCM computer module, the mechanic told us that the circuitry was working, but that the horn was working only intermittently, the radio and clock were working, and that the windows would work once he installed the regulators. He also said that he would do all the wiring repairs, computer programming with factory updates, and that he would have the remotes and micro-chipped key along with the factory installed GM PASS-Key theft deterrent system "re-learn the procedures". Something obviously went very wrong during the repairs in that immediately thereafter, the factory-installed theft deterrent system was no longer working as it did when the vehicle was brought into the shop. The alarm keeps going off at eratic and impromptu times, beeps irregularly, etc. We brought the vehicle back THREE times and the mechanic continues to state that he fixed the problem. In the end, we learned that he could not fix the problem and replaced the factory-installed GM Pass-Key theft deterrent system with a cheap aftermarket alarm system (nothing like the original AND this too, is not working properly). I am very concerned about what this mechanic did, not only to the car and its security, but to the loss due to same in its sales value. 1) Did the mechanic correctly analyze by thinking that the car required a BCM computer module for the above-mentioned problems? If he did, should he have installed a Chevrolet-authorized BCM computer module, i.E, would a Chevrolet Camaro BCM computer module replacement part be more compatible to re-learning all the Chevrolet Camaro factory updates, key, vin, and security system and have prevented or averted problems with the factory-installed theft deterrent system or could the problems lie in the fact that he may have irreparably damaged the factory-installed theft deterrent system during the electrical re-wiring? SHOULD THE MECHANIC HAVE INSTALLED A CHEVROLET-AUTHORIZED BCM COMPUTER MODULE?
2) Front tires were replaced with 235/55R16s. In checking, I learned that these tires were the
factory-installed tires for the 2001 Chevrolet Camaro V-8, Z28 and that the 2001 Chevrolet Camaro V-6, Base, my son's car, should have been replaced with 215/60R16. Kindly advise.
Thank you.