Speedmaster Exhausts For Euro 5 Speedmaster...

I did not do myself, but know some guys using other exahusts. Dr. jeckill and cone engineering, also on bobbers (speedmaster and bobber 100% share mechanics)

Triumph even sell an alternative exhaust made by V&H. And you can see many videos of owners showing other pipes.

For some it would be interesting to remap the ECU to get best performance, but no danger to damage the engine.

There is someting in the initial exhaust manifolds named "lambda probes" that are used by the ECU to adjust explosion to the actual function of exhausts.

That what you say sounds like the kind of bullshit some low talented brand dealers argue to avoid having to deal with options they do not know.

 

I've had an X-pipe and a pair of Hitchcox drag pipes on my 2021 Euro 5 speedmaster.
The limiting factor will be whether your bike's cat is welded to the exit tubes or clamped. If it's clamped then any compatible after-market pipes will be possible. If it's welded then without major surgery you're stuck with what's there.
No ECU problems at all altering exhausts although if you start removing or altering engine sensors then the anti-tamper software now built into the ECU will illuminate the Engine Management Light....