I don't usually advocate circumventing certain things, but in the case of a portable generator, "ground" is a pretty loose concept anyway, and really doesn't mean a whole lot...
Have you considered simply establishing your own reference downstream of the genset? It isn't like RCD/GFI requires a reference to actually operate... Personally I'd keep it in the mix and just take away the power and bond the system ground downstream. Hot and neutral are really only what they are because of a definition (determined by the bond)... especially in a genset. So really, there's no such thing as "reversed" in that case. This isn't to say I don't understand your findings, just that there are simple ways of working around it (one viable means, being what you've already done)
Like I said, not really advocating defeating anything, but when there's not really anything to "defeat"... know what I mean?
I've seen arguments on both sides of the fence when it comes to how to handle grounds and portable gensets. My stance is "float". Reference it correctly to itself but carry the power away without it.
This is essentially what was done with the truck genset... The actual OEM ground connection isn't anything more than a bond to the engine, which I discovered wasn't part of anything else anyway in that particular case, so trying to sink errant current into ground downstream doesn't do anything but make the internal chassis go hot to whatever degree. In my unit, there's also not really any exposed metal anyway aside from the plate the outlets are mounted to, the rest is all sheathed in plastic. I ran ground bonds out with the original intent of bonding truck frame and genset engine together but decided last minute this would mean precisely squat, and in the event of a fault, would only serve to cause possible internal damage to the generator. Instead, I only take away the 120 and established the ground for it on the power board. Hasn't been any issue with doing so.
Also, my genset doesn't have RCD/GFI built in, but I used them downstream. They've saved my neck at least once, so I absolutely don't recommend going without them, just possibly "relocating" their position electrically in the system, depending on need.
Either way, it's not a willy nilly consideration. Safety should of course remain a top priority, whatever form that takes.
(Put another way, don't listen to me lol)
Steve