As I understand it it should be straightforward to adapt CKPatch to work with both demo versions, once you know the offsets of all the items of interest in the game executables. I'm quoting the wiki:
unfortunately I don't know much about coding, so I hope someone can help me with this task.CKPatch has a modular design; the Parser, Patcher and Loader units in the source code are completely independent of Commander Keen and can easily be reused to write patching utilities for other 16-bit real mode DOS games.