R7500v2 is apparently so close to the R7800 that the same process should work okay.
You should be able to find the relevant OEM source files, like you already linked one. Those files pretty much provide the basis for the assumption that it is similar.
My test of flashing modified openwrt, filling overlay with garbage, flashing OEM and testing basic functionality, flashing normal openwrt and looking closer into partition contents like VPN cert, should be sufficient proof.
The long forum discussions linked in 1003 show the commands that I used.
E.g. Netgear R7800 exploration (IPQ8065, QCA9984) - #1147 by hnyman
Ps. Note that for looking into recreated OEM certs etc., You will need to use unmodified vanilla openwrt, so that Netgear partition is visible.