apeja in its current state is a bit too specific for toki pona. it feels kokosila. one can simplify the feelings of guilt and shame to get to the core of what they are, instead of using apeja. if you have guilt, it is a feeling about your mistakes ("pilin pi pakala mi"), and being guilty is that you confirm the mistakes are from you (pakala li tan mi). disappointing your parents could be said "mama mi li pilin ike tan pakala mi." my parents feel bad because of my mistakes. dishonoring them could be "ona li ike lukin tan pakala mi." they look bad because of my mistakes.
so here's a proposal for a meaning expansion based on its SP glyph that should broaden and give it more use without making it a very different word: exclusion. that something is not involved.
in this way it acts as an antonym to kulupu, kan and kepeken and is also a preposition, thereby meaning "without" as opposed to kan's "with"/"alongside" (the collaborator preposition: that someone is involved in the action but not in what way) or kepeken's "using" (only to say a tool is not used, not the method prep or "using" in general).
in content word, it means "excludes" as opposed to kulupu's "groups together" or kan's "includes". and "lone wolf" or "exception" as opposed to kulupu's "group"
mama o! mi tawa apeja luka! "look ma, no hands!" (lack-of-tool prep)
ona li apeja akesi telo e nimi akesi. "they exclude amphibians from their definition of akesi." (trans prep-verb)
mi pilin apeja. "i feel excluded" (content word)
sina pali ala la mi pali apeja sina e kalama musi! "You did nothing, so I made the song without you!" (collab prep)
example sp sentence using extended apeja:
ona li {apeja akesi_ telo_ e nimi akesi