Overstress,
If ya got a company designator (such as 'birdseed') then ya callsign should NEVER be abbreviated. (yes that was a full stop)
Having said that a few aircraft have flown for years using non-standard callsigns. (G-LEAR, G- 4 eyes, and all of them strange US birds that fly with the aircraft type as the designator ['Falcon 8 100 E... etc])
Chatters