can or can't I do this?

[sickx]

As long as you are actually heel-and-toeing properly, there is no problem with the clutch. However, I question why you are doing this simply to brake--the purpose of H&T is to match the lower gear in preparation for a slower corner.

It will get quite expensive to do this simply for braking, as engine/tranny bits are far more expensive than brake pads.