1 - Go on dedicated server, download custom mission (like Altis Life), and spawn as a player,
2 - Edit the mission,
3 - Restart the server while connected on it,
4 - Connect and load mission files,
5 - At the end of mission files load, it can randomly kick you out of the server with written in chat : "Max : Max uses modified data files - C\Users\......\AppData\Local\Arma3\MPMissionsCache\__cur_mp.pbo".