gms_team_join

team id works as a "keyword", like image_speed (per example).
Yes it can be choosen, it varies depending on the team that your joining.
A simple script including this extension would be something like
if host = true{
gms_team_join(1);
} else if host = false {
gms_team_join(0);
}
on both cases the "team id" is evidenced as 0 and 1.

Hope it helped :)