The net charge and spin multiplicity are directly reflected by the wavefunction information recorded in the molden file, so you do not need to explicitly tell Multiwfn these information, you just need to make sure that you have specified correct net charge and spin multiplicity in your ORCA calculation.

I have succesfully calculated RESP charges in Multiwfn.
The system is an uncharged molecule with an unpaired electron, so multiplicity =2
I used as input a molden file, generated in ORCA.
I can see from the Multiwfn messages that multiplicity 2 was used.
Just to confirm. Is it not necessary to tell Multiwfn what the charge and multiplicity for the molecule should be?
I was not able to find information on spin multiplicity within RESP in the manual.