Ah, interesting.
Perhaps dumb question - did you alread try this arrangement?
Generator without LOM, UPS deactivated and wide input range? I know - on some systems (like in mine) not all options are available.
Perhaps another dumb question - have you already tried with ESS, grid code and the quattros set to “charger only” mode? I haven´t on my system - but then they should go into passthrough/“dumb-charge” mode. That could be remotely enabled and disabled. It would have to be switched in the following order to prevent power loss on the output:
first “inverter only” → then changeover to generator → then charger only to allow charging → then, when finished back to inverter only → changeover to grid → then “on”.
Regarding feed in AC out - it´s different because the quattros are the grid-forming part and there is no LOM and no need to try to sync on something else. But AFAIK, AC PV control via frequency control is then active, if AC-PV on output is set as enabled as a must-have safety option.
Regarding your question - i dont know about a method for simulationg ESS behavior like DC PV feed in without ESS by an external PLC or so. Neither i know about a method to switch grid codes remotely.
I think the question “why it is not possible to use a generator if i have grid code enabled?” is not easy to answer - becuase it is. In my case it works and victron is even promoting it. The difficult part is, why your system is so picky about it.
Btw. - the UPS-thing was power-quality related and had nothing to do with capacitive reactance from he UPSs. We checked that out by using a power quality analyzer that told us voltage and freq. were in the ball park region to work and power factor was ok, but the waveform was crap and was then partially pulled into shape by the misused freewheeling motor. 