When I join a new game through a lobby, I can select my merc via F1/F2/F3 in the respawn menu. But when I join a game that’s already in progress, I can only press Deploy and it doesn’t let me select my merc. So far I’ve always used that merc until next respawn or I outright suicided which gives you -150XP 
Is there a way to select a merc before deploying into an ongoing match?