Modifying a completed symbol with a behavior

I realise that text can be appended after completed symbols using a completion behavior, but can this include modifying the symbol itself? R has an oddity that setter-type functions have names that include assignment syntax, such as dim<-. I would want a static completion for this symbol to show in the completion list as dim<- (to distinguish from dim, the equivalent getter function), but the full inserted text should actually be dim($[]) <-, which requires the last two characters to be removed before appending text (or the insertion to happen in the middle). Does the API allow this?

Thanks in advance!