KJ, I understand and respect what you are saying but I am not sure if we are talking about the same thing: I dont refer to a "built in" extension as in Jeanette Lee's jacoby cue that is always on as part of the cue and you unscrew the butt to extend it, I mean a screw in extension like in snooker mini butts. It is not on all the time... only that shot in 20 when you screw it on.
Also, it requires no damaging or alteration of the cue just a bumper that has a female thread to accept the male one in the extension. You could always return to the original bumper and the cue would be in original condition. This extension is commonly used by players such as Mika Immonen or Marcus Chamat.
Maybe you mean that this modified bumper would be really overweight, but being only rubber I tend to think it would be close to the original bumper (0.2~0.4oz). Unfortunately, I don't have the weight for mezz's bumper. I can compensate for small weight differences in the bumpers by using a different weight bolt, if necessary.
I don't have a southwest either
but I don't think exchanging a bumper would be sacrilegeous since it is not a permanent modification; similar to using a different shaft.
I just want to try it to see if it helps in certain shots... if not I can always return to the original joss bumper. The main problem seems to be that mezz's bumper thread is not the same as joss' bumper thread so it won't fit straight away (or at least that is what j&j told me).
Does this make more sense?