According to the 2006 TRD
Parts Catalog, there are four different TRD
'00-'05 Celica GT:
PTR08-20000-08 Muffler for use with extend tip for use with rear valance (such as TRD
'00-'05 Celica GTS:
PTR08-20000-07 Muffler for use with extend tip for use with rear valance (such as TRD
The main exterior differences between the GT and GTS TRD
mufflers are the piping locations and the hanging bracket location. TRD
Exhaust systems are "bolt-on" replacement exhaust parts.
If you purchase correct TRD
exhaust for your vehicle, you can install it yourself in under an hour, using only a vehicle jack (I recommend ramps & wheel braces). I managed to swap out my stock exhaust for a TRD
exhaust in under an hour, by myself, using only the tools & directions listed in this link:https://www.celicahobby.com/forums/ubbthreads.php/topics/18979/Exhaust-How-To-Remove.html
NOTE: I did not have to purchase a new set of rubber hangers since I did the swap at less than 800 miles, but if you needed to, they will set you back less than $20 at your local PepBoys/AutoZone/Napa Autoparts...etc.
Also review this link:https://www.celicahobby.com/reviews/exhaust-systems/p61-trd-sport-exhaust-system.html
Any other exhaust that is not "specific to your year and trim" Celica, will probably need professional installation by someone with welding tools.