Replacing LS&GCM
As ever our French friends set us an example we might wish to follow. 20 years military service is recognised by admission as a Chevalier of the Legion d'Honneur (titre militaire). This would equate to something like MBE (military division). Of further note, all must enter through this 'door' : ie you can't be a officer (officier) or commander (commandeur) until you have been a chevalier.
Admission is normally based on a simple application stating that one has completed the necessary 20 years. If your conduct has been good enough to still be in then award follows. Subsequent promotion requires a citation of some further merit which might include time or specific action, or both.
It would not be difficult to adapt the Order of British Empire (Mil div), replacing the LS&GCM, including officers (and getting more ORs into the Order).
Regards
Batco