go to address $26C and replace the data with 4C 6C 82 to make that change.
That's a good start, it stops the demo. But if you press start after 500 or so frames, it still goes back to the title screen as if the demo was playing, rather than go straight into the game, so there's something else happening - in fact, I think the OP had the exact same situation when he started the thread.
After making that change, you can see in the RAM that $7A2 still decrements, so clearly it won't let you start the game if $7A2 is zero. So I did a read breakpoint on $4016 - the controller 1 register - to see what would happen when I pressed Start before the demo starts. I predicted it would store the controller value somewhere, then check $7A2 to make sure it's time to start the game. Sure enough, it stores the controller value at $6FC, then first checks if it's $10 (Start button pressed) then does a Branch on Equal with $7A2 - in other words, jump to the reset routine if $7A2 is zero, otherwise Start the game.
So the simple option is to go to $2EB in the ROM and replace F0 EC with EA EA. Now the game starts when you press Start, even if the demo is playing (why couldn't Nintendo have done this in the first place?!). Combine that with what I quoted from KingMike at the top of my post, and you've got no demo and no reset problem. There you go!