Opting out of Firmware updates in Endpoint Manager

Is there a way to opt one extension out of firmware updates from the freepbx server?

We have a phone that we need to test a beta firmware on. We’ve created a new device template just for that phone. However the only firmware options are Firmware Slot 1 (which we use for the rest of the phones) or Recommended. Both seem to give the phone the standard firmware.

If we replace the firmware, its replaced by the server (old) firmware automatically.

Is there a way to specify “None” as a firmware option?