Yeah there's no loadout changing in-game. If you Abandon Match, it starts a 90 second window where your spot on the ship is held by an AI, giving you enough time to get back in if you accidentally left or your comp crashed. If you change your class/loadout in that time, you'll see the Resume option at the top of the main menu, or you can go through the Matches list and find the same match to jump back in (the Resume button is way faster).
As a pilot who often changes ships but forgets to change loadouts, I do this all the time. I either back out right when the match starts, or immediately after our ship goes down. That way I know I have a few seconds to spare where it won't hurt us.