Sure, here's a patch for Castlevania PRG 1.
Why, though?
Edit: Oh, you're the fiancé hack person. Just in case you're working from some modified ROM where this wouldn't work, the demo is triggered when $001E in RAM reaches zero on the title screen. When $001E is not zero, it branches to code at $B858. So I replaced the code that decrements $001E and the branch with a jmp to $B858. The jump means it ALWAYS goes where the game normally only goes if the counter is not zero. So the code that runs when the counter would reach zero in the real game (the demo stuff) never runs. Good luck!
And let me know if there are any problems with it, I spent like... five minutes on it.
Edit2: Oh, you can do it with a one byte change. $B858 is an RTS, so you can just change the opcode for dec $001E to $60. Oh well, I'm not uploading a new patch.
