As far as switching I'm not sure what I would do if if were you. But running 2 on the same output can be done the biggest issue I see is one I'm currently having. With my enclosures stacked (with a small gap) the enclosure on top is getting heated from the enclosure below for now I'm getting 92 degree floor temps on the top enclosure from the 80w rhp in the bottom enclosure. Which is fine for my Bp (in the top enclosure) but my boa likes it a little cooler.

So basically what I'm saying is if you stack enclosures it may be difficult to regulate heat in one of them using one tstat.