“All graphics, fonts, music and sound used in the game must be available on OpenGameArt.org or made available OpenGameArt.org by October 31, 2018 11:59 PM CST. ”

“However new works, derivatives, expansions, extensions, addendum, etc. are allowed so long as they are made available on OpenGameArt.org”

I think the rules are clear in that regard. Everything should be uploaded. I would not  upload automated changes like gray-scaling, mirroring, reordering or splitting sprite sheets, filters etc. … everything you could also script with your engine.

If you think it’s really minor, it could be an option to just leave a remix comment on the original instead of doing a full new  submission.