Potential for damage?
 

If I need to put an extension directly off of the servo horn, what kind of carnage will occur? Hitec 645MG(I think) servo w/aluminum horn.

It is on a FOFF rig. Just trying to get some more steering.

as long as you set your end points properly it shouldn't make much difference. i actually just did this to my servo horn on my XR10 today. if you're gonna have your rig setup to go fast, you might want to consider a servo saver though. especially with an extension on the servo horn.

You will decrease the torque from the servo to the wheels and it will make that servo horn easier to strip....

+1, additionally, it makes it easier to strip servo gears if you shock the front wheels.:cry:

X3.
I have added a longer arm on a 645 in the past. Output got a little weak.
But that extension acts like a big lever (moment arm), so a shock to the front wheels will be a lot rougher on the servo drivetrane.

Im not sure how your rig is setup but you can get the same effect by making your tie rod closer to your c-hub pivot point. That would also have the same levering effect over the servo as a longer arm.