I created a linear bootstrap.dat for the chain I'm synced with near height 1314626.
You can download it
here.
Next, I'll see about trying that thing with the Network ID change as a proof-of-concept.
I have found no code that allows the pchMesssage to be changed after compilation. If its there, then great.
I've already tested changing the pchmessage code. It works (maybe I should have mentioned that like a week or so ago). All nodes not in line with it don't work with a wallet compiled with it, though the blockchain is still fine. The wallet doesn't even consider any nodes w/o the same code.