What about having something fade, it looks like it is changing value, but it is just the alpha.
we did it in Aspect Arcade (some of the particles fade out). imo it's really more of a grading risk than anything, as you're being graded on Bitness -- in other words how 1bit your game is -- so in a sense it's up to your fellow competitors if they accept alpha values as allowed. Bitness is ultimately just 1 of the scoring categories.
but, to more directly answer your question, alpha manipulation would break the "1 bit" rule.