I'm certainly no expert on natural banjo skins, but it does seem to me that you are experiencing a humidity related loosening of the skin. My primary instruments, wood flute and concertina, are loving this humid summer we have been having, but I know the higher humidity is not universally appreciated by instruments. The method you are suggesting sounds a little extreme. I would consider loosening the strings, then taking the banjo into a fully air conditioned space (lower humidity) to see if the skin tightens up first. Following that, attempt to keep your banjo in a space with lower humidity to preserve the tension on the head. I know that my 5-string used to have a large number of bolts that could be tightened around the rim to adjust the tension on the head. Does yours?
The C&F is probably not the best place to get info on banjos. Why not check here:
http://www.banjohangout.org/forum/.
Good luck.