It is possible to set up crew endorsements per a tail.
When defining a new endorsement (section Settings > Crew Endorsements), click 'Aircraft selection type' to choose between: per a type or per a tail.
By selecting 'per a tail' Leon will show all active tails.
Once a new endorsement's details are added, mark appropriate tail/tails and save changes. On the main list of crew endorsements Leon will show marked tails.
Leon will show endorsements defined per a tail only for flights assigned on tails to which such endorsements have been linked.
Example below shows a flight with the aircraft H-ELMT, which was not assigned to the endorsement OPC - Leon does not show it on the list of the required endorsements.