That is what I did with an Octagon Quad. The 4 connections are 12V, Reference, H and V. There is a mod on the BATC WiKi ( https://wiki.batc.org.uk/Es'hail-2_LNBs_and_Antennaes ) that you can do to remove a resistor that sets permanent H or V on an output. I only modified 1 port to do this.
The port used for the reference is disconnected from the original circuit. The crystal is removed and the 25 MHz fed to one side via a capacitor from the scoket.
The DC in port is unmodified. You could cut the IF track but it is not necessary.
The two IF output ports have had the DC feed inductor cut. This is to avoid DC appearing there but also prevents the 22kHz LO switching so you may not want to do this is you need that facility, put in a DC blocking cap perhaps.
On one If port, it does not matter which, the resistive divider was modified. The chip detects 12V or 18V through this divider and all you need to do is make it think it has 18V when there are only 12V by adjusting a resistor. The only challenge if figuring out which resistor on each type of LNB, but a bit of probing with a multimeter should help.
I want to modify a OPTICUM LRP04H, but the Heiner proposed did not help me ?
It semms to be a good idea, to use a quadr lnb and want to test it.