I have seen a gravity mod that allows you to change the direction of gravity, it works with 1.12.2, although I cannot port or mod.
Are you talking about Up And Down And All Around? I tried this mod but its completely broken. It constantly crashes even when its the only mod loaded. The mod author has abandoned it and probably wont be coming back(although just a guess). Believe me i have searched everything. I tried porting it but something just doesnt work for me. Thats why i asked others for help