I don't think that's an adposition; I think it's an adverb -- i.e. "screw up": screw how? "up" (metaphorically). This would of course drastically change the meaning with the switch of an adverb:'
"You screwed up the computer because you didn't screw in the hard drive". Two entirely different actions, same verb. Not the same verb in meaning but in orthography.
First of all, your example uses two words as if they were the same word.
Screw and
screw in your example are two separate words, which happen to be both homographs and homophones. But their meanings are entirely different. The first screw approximately means "to foul, damage, or otherwise molest." The second screw means "to attach with screws." I think you are mistakenly believing that up is modifying a common word (in this case, screw) so as to effect a meaning change, when in fact the two are different words.
That being said, if we are really going to decompose this to the atomic level, what we're actually talking about here are
phrasal verbs, which are essentially compound words. So your use of "screw up" is a compound of
screw (to foul, damage, or otherwise molest) and
up (generic, analogous spacial preposition indicating a general increase, as if filling an empty vessel), while your use of "screw in" is a compound of
screw (to attach with screws) and
in (specific spacial preposition identifying a specific location).
Long story short, "monkey up" versus "monkey around" are phrasal verbs that are effectively the same for all intents and purposes. Both of these phrasal verbs derive their meaning from their primary root "monkey". And indeed, those who claim that there's racism in the term "monkey up" predicate that alleged racism on the use of the root. The prepositional component is only changed here for grammatical purposes, much like inflected word endings can make words plural, past tense, etc, without substantively changing the meaning of the root. The differences between "monkey this up, monkey around, monkey about, monkey with" or comparable terms are merely grammatical in nature. They all have the same essential meaning.