Yes, I believe you can do 121 exchange at service center for gap issue. But first they have to check the stock if its available for exchange. (I think their re-stock volume is very minimal, due to HTC current problems)
It may take 1-2 weeks and also if they have a stock.
If they don't have the stock, I am afraid you have to continue waiting till they have it.
So my suggestion, wait til the stocks are replenish only then do an exchange. (This is what ill do aswell,if my device are suffering from defects)
Edited.
You can also contact HTC team straight rather than contacting SiS for clarification on warranty (eg gap,dead pixel)
and also be firm when claiming your warranty,use your anger if you should.

Source of this,I contacted HTC team previously by e-mail.
Edited again, correcting my sentences and grammar.
This post has been edited by noookiller: May 27 2013, 11:25 PM