I wonder if the toa nuva will go through protidermis again? It would probably make them strong enough to defeat the bohrok-kal and the rahkshi. Is that even possible??

The Toa Nuva aren't going to be transformed again for a long time if not never.

In comic 8, it says on the last page "Now and forever more, we are Toa Nuva" So I think that's good enough proof that the toa won't change again. GregF wouldn't have put that there if the toa were going to change in the future.

They won't change again; they'll find some other way to defeat their enemies, probably through their teamwork. If they did go through the protodermis again, I think fans would start to get bored with the whole "changing" process.