Change Skyboxes for Marble Blast Platinum?

Hey guys, I have been playing MBP for a while and I recently wondered if I could theoretically replace the current Skyboxes (used by default- I think its an ocean) with the original MBG skyboxes or other custom ones?

You can, probably by simply overwriting the skybox images used with your own. Beware that the anti-hack (and probably the launcher) will most likely attack you for it, reverting it back.

Can confirm that the launcher will revert the skies if you edit skies.zip. You may be able to get away with extracting the zip and editing the skies with the original zip in place, can't confirm that though.
The anti-hack shouldn't care about skyboxes, so you should be fine in that regard.