Originally Posted by st50pan
...Can I swap my '03 TSSM and ECM into the '02 so I get the alarm function back? Can I just do one or the other? I have both manuals to reference. ...
Theoretically, yes you can swap either or both. If you just swap the ECM you'll need to "marry" the '02 TSM/TSSM to the '03 ECM as explained in this scanned image from the EDM (= Electrical Diagnostic Manual):
(You should get an EDM before messing with this.)
The change from '02 to '03 was the position of the IAT (intake air temperature) sensor. This was moved from the front cylinder intake runner to the upper air filter cover. The '03 ECM will be programmed with a calibration file that assumes the IAT is moved to the new location so you'll need to move the IAT. Moving the IAT isn't trivial since it's a pain to remove and then you need to plug the hole in the intake runner. The factory relocation "kit" (P/N 29434-01A) uses a new IAT sensor (P/N 27388-01) and a jumper wire to allow the original wire to reach the new location.
The '03 ECM calibration is also programmed with the V.I.N. of the '03 bike but this doesn't affect operation. If you wanted this changed you'd need to go to a dealer and have the ECM re-calibrated.