This feature is, essentially, intended for pures who have slightly overlevelled to correct that mistake?
What about mains that slightly overlevelled to correct a mistake?
Can you help a main since you helped pures? u/Jagex_Stu
Unfortunately, no, there isn't anything I can do to help you. Content developers are not permitted to modify individual player accounts, so that Player Support have exclusive control over account management.
You could try contacting Player Support https://support.runescape.com/hc/en-gb/p/contact to submit a lost item claim. I suspect trimming an undesired skill cape wouldn't qualify as a missing item, but eligibility is Player Support's decision (hence I'm unable to intervene).