Can Linux custom images be made from VHDX files of custom installations?

Is it possible to install Linux (in this case Rocky 9) in a Hyper-V Vm, customize it (install and configure software, etc) and then convert that for use in MAAS? The Custom image docs are very very thin but it seems like MAAS (or Packer-Maas) only wants install ISOs.
If this is possible, is there documentation on it anywhere?