From everything that I can find, A2 antagonization via yohimbine results in little if any significant negative receptor effects in regards to density/count and affinity characteristics. As an FYI, there are other A2 antagonists which are noteably more 'potent' than yohimbine, and do seem to cause changes.
A good read on the subject can be found here =
http://edrv.endojournals.org/cgi/reprint/16/6/716.pdf , although it is from '95 and some of the quesions raised in the documentation have most likely been answered since publication... (i.e. influence of sex hormones on the A2).
In the end, I would still agree with Dante's recommendation of 4-6 weeks, as the real world practice/use can return much different results despite a study's conclusions. In fact, it has been observed in some that fat re-gain has been quicker/greater (in regards to the applied sites) after one has been using for longer periods of time... which could probably be accounted for, at least partially, to some kind of regulatory mechanism(s) of the A2's.