First of all, why would you (or the person playing the game) want to turn Sonic 2's HUD off? It's too useful. Second, adding a pause menu would be complicated and should be done yourself. The best method would most likely be adding a new game mode based off of either Sonic 1/2 beta's level select or Sonic 2's options menu. You should make sure it doesn't clear any of the level data when accessed. Third, the basic idea for change options that you had could easily be done by checking for button presses while the game is paused (which is already done in Sonic 1 [and possibly other games] through the pause cheats) and make it so when the button is pressed, a RAM address is changed. If you toggle it on or off, you need to check if the RAM address is a certain value first and make pressing the button change the address accordingly.