Triumphrat

How much would it affect the handling of a 1996 Thunderbird if i were to back off the adjustable coilover to drop the back about an inch? Also, is it just as easy as that-backing off the tension on the spring?

I have thought about this too,even went and bought a C-spanner for the job, I have just never got around to doing it. Triumph recommend that you dont adjust it. It's in the owner manual somewhere.
I'm still gunna give it a try when I get a bit of time.

Slinky

Another option is swap the suspension drop links for a pair from a Legend. That will lower the rear without softening the springing.

__________________
"You can't fly with the eagles if you keep scratching with the turkeys."

MickMaguire

It's likely to make the back feel very soft and under sprung. You may find that the spring comes loose first.

__________________
Mick...