A slip on normally does nothing for performance in either direction. You don't need a tune after, and you won't feel a difference in power. Its just a noise and sound mod.
Removing the slip on and running a tip that ebay sells as a muffler, that's different. Also, toce and taylormade are known to loose power in older models from actually being more restrictive then stock.
'06 F4i: racetech front springs+valves, ohlins rear shock, steel brake lines, 'mura slipon, 87K miles
'08 600RR- steel brake lines, shorty brake lever. Stripped track bike.
'15 1000RR- Flapper mod, 08-11 gauge swap, hotbodies fender eliminator