'08RK... When I placed the Supertrapp slip-ons on the RK here I asked the service gang at the dealer about this. My personal experience on a number of makes is FI can typically handle a slip-on only mod OK. It is when the air intake or headers are changed where the FI can be "challenged". The dealer response was they have seen bikes come in for slip-ons only and leave in fine shape after some testing, and they've seen bikes come in for the same with it clear an FI remap would be helpful.
Perhaps you could try the Thunderheader slip-ons and see how they perform. Is there major backfiring? Are there other indications? FWIW, the Supertrapp SE's (Were the Screaming Eagle touring slip-on source) have worked fine here without any need to tweak the FI.