I have a old model 1100 Trap. Is it possible to re-barrel, re-stock and put a chamber extention to make an effective tactical weapon?

The "trap" and "skeet" marked receivers are the same as standard field grade ones with 2-3/4" chambered barrels. Stock and barrel swaps are pretty easy for the most part.

The trap models are worth money. Don't change with it.

You're better off buying an 1100 Magnum or even better still an 11-87 for tactical mods.

Both of those models feature receivers that  are 1/4" longer than the standard, older 1100 receivers to
accomodate the 3" chambered barrels.

Get a used 11-87 field gun cheap, and convert that instead