Thread:Digi/@comment-265341-20150811155032/@comment-5951231-20150929212028

Momotaros can become Den-O on his own in later installments, but still needs Ryotaro to activate Super Climax or Liner. He can only do this when he has his physical body, so post-Decade.

So we could say it is Momotaros on his own, thus form change is impossible.