Well, it's not common that officers serve different masters serially as if they were mercenaries, even collecting different noble titles from different monarchs.

What's common nowadays are fighting military advisers and military observers, as well as participation in small wars and peacekeeping instead of getting involved in conventional warfare.

I saw some hints that some countries appear to send otherwise implausibly small military observer teams to UN missions. This appears to be a kind of military experience gathering scheme.

Finland has seven such tiny missions now as far as I know, for example.