well, context.. poster wants louder/different 'exhaust note'..
if it was about emissions and changing 'exhaust note'
perhaps add-on or retrofit cats such as akrapovic,
additional to, the slip-on..
eu4/5 will mean cats closer to the combustion process
thus further forward of mufflers/slipons [anyway]..
thus cbr250r slow to light muffler cat is already
virtually obsolete,, in terms of emissions laws
and evolving motorcycle design to meet them..
fuel injection, cats, ride-by-wire, variable valves,
and so on, are here or soon will be..
the simple small single 4stroke motorcycle [even]
will join other petrol burning engines and dinosaurs..
for now, for me, my engine is 1/4 or less the size of
cars, more efficient and cleaner, esp in traffic etc..