Can you load/open a MAP that is already on the game?

I think that the title says it all.

Yes: SRB2 stores its maps in the file zones.dta, and you can open it just like any other wad file. However, you should make a copy of zones.dta before doing anything, because any modifications to zones.dta or other core wad files such as srb2.srb and sonic.plr will prevent SRB2 from working.

Thank you!