Formally the Multi RS only support VM-3P75CT energy meter.
But I was wondering, can I use a HomeWizard P1 dongle with e.g. a dbus-serialbattery driver and a Cerbo GX?
Or is there an other alternative?
For use as an ESS it is not wise to use an unsupported/software based meter. It is critical to reliable operation and modifications like this are not 100% reliable, any timing issues can cause instability.
Same reason victron do not support virtual meters for this role.
It is fine for measuring loads and third party accessories but not as the basis for a grid-meter.
I am using the HW P1 meter for more than 2 years on two systems. Once in a while (if KPN is messing with my router again) I get a warning message “Grid meter is missing” But it recovers by itself as soon as P1 is available again. But as nick said: you are on your own!
For a dbus driver search the net: P1 dbus homewizard github
FYI I am not using MultiRS (yet) I am using MP2 and A CerboGX.
Indeed, nothing stops anyone from doing this, people very much do, as you pointed out. You just need to understand and accept the risks, should they materialise. Not new territory for a capable DIYer, but a potential hidden surprise for the inexperienced.