Remove virtual machine options with qm

`qm help set` lists you all possible settings along with the valid and default settings. Setting it to the default should be equivalent to unsetting in most cases. For settings like -cdrom you could try an empty string.
 
Hey, thanks for the reply, I ended up using:

# sed -i '/^host/d' VMID.conf

the special '--delete' also works, though you'd have to call it once for each hostpci device.