The multicellular and aware stages are defined by having certain traits. So, if you remove these traits, will you revert to the previous stage?
Removing traits will cost mutation points just the same as any other change. Also the stage transitions will be made as smooth as possible. So technically you can go back from certain stages, but in practice it has very little practical implications.
Will you be able to continue the multicellular stage as a single syncytium, and will you be able to reach the aware stage like this?
AFAIK, there’s a really hard limit to the max size of a single cell on Earth. Due to all kinds of things like the risk of a single rupture of the membrane killing the entire thing.
It isn’t very realistic to have big things that are a single cell. Also the defining feature of multicellularity is that you can get a lot bigger and you can start specializing the different cells to do different functions.
But what if you made a really small organism?
Here’s a list of the biggest single cells discovered on Earth. It seems the largest bacteria are 0.75mm, the largest cell with a single nucleus can be 10cm tall and the largest multinucleate cell can have fronds 3m long.
So I think single cells can get quite big.