pdh
First off, Welcome to the GBO forums!
Lots of good people and information here.
I haven't heard of the hammer extensions voiding the TC warranty!
The only thing (negative) that I've heard is that with the extra weight on the hammer, you can get misfires.
Some people have corrected this by simply removing the hammer extension. I did!
Others have changed the hammer spring to a new heavier spring.
Now there is a third option, it's called the "Swing-Hammer" and from what I hear, you can send your receiver to TC and they will install it for around $75.00!
Again, Welcome!