The answer is actually in Create Demiplane. It says, in part -
You can use this spell to expand a demiplane you created with create lesser demiplane
This is the rider from Create Demiplane, but the other spells in the series have the same basic text.
So, no, Create Demiplane will not affect a demiplane created with Genesis, or in fact, any other demiplane than one you yourself have created with a Create Demiplane spell.