Can you elaborate more on "make the game act like a legacy version"? The word "act" and your (lack of) description for "legacy" is super vague and the combo could mean different things.
Is it graphical-wise? Is it gameplay-wise? Maybe both?
Are you trying to make objects do something different to what they normally do?
Are you talking about making OpenGL look like Software?
Are you trying to replicate something from past versions of SRB2?
Are you trying to make the game look old like DOS Doom?
Are you trying to make something related to something outside SRB2?
What is "legacy"? What are you trying to do?