The short answer is NO. Mosaic does not have the ability to have its sACN priority dynamically changed in runtime like you can with Paradigm.
If you need to hand over or take control to/from an external device, such as a console, there are several ways to do this without having to dynamically change sACN priority.
Set the sACN priority higher on the external device (sACN priority Mosaic default is 100). When the external device needs to take control simply turn that device on. If Mosaic needs to be in control simply turn the external device off.
Setup Mosaic triggers to enable/disable the controller's outputs. When the external device needs to take control a trigger can be sent to Mosaic to disable its outputs. When Mosaic needs control back the external device could send a trigger to re-enable Mosaic's outputs. The external device should release the channels as well.
Download the Park module within Mosaic Designer. This will allow the external device to park all addresses in Mosaic to 0% so the external device can have full control of the rig. Of course once Mosaic Needs control all of the addresses can be un-parked as well and the external device should release the channels.