According to Law 3 of IFAB's Laws of the Game, a team may substitute players at any stoppage of play, including corner kicks.
Many youth leagues allow for an unlimited number of substitutions. In order to preserve game flow and prevent this from being used unfairly by a team ahead in goals to waste time, such leagues will limit subbing opportunities. In these leagues, subs are not allowed when play is to be restarted with a corner kick, free kick, penalty kick, dropped ball, or the opposing team's throw-in. The throw-in restriction is usually waived if the team taking the throw is also subbing.
If your league allows more than three substitutions per team, check the rules for subbing restrictions.
Any player from the kicking team.
A corner kick is awarded any time the ball crosses the goal line after being last touched by a defending player.
If the crosses the goal line (but not into the goal), and last touched an offensive player; it is a goal kick. It is a corner kick if it was last touched by a defending player.
Yes, they have.
No you cannot. In order for a player to be offside, that player has to be behind the ball and behind the 2nd to last defender. On a corner kick, there is no way to be behind the ball unless that player goes off of the field.
Yes. A player may score directly from a kickoff, goal kick, corner kick, direct free kick, or dropped ball. A player may not score directly from an indirect free kick or throw-in.
1984
You cannot be offside from a corner kick
clearance
If it does so above the crossbar and the last player to touch it was an attacker, then it's a goal kick. If it does so above the crossbar and the last player to touch it was a defender, then it's a corner kick. If it does so below the crossbar and it came directly from the defender's goal kick, corner kick, kickoff, or throw-in, it will be no-goal and a corner kick for the attackers If it does so below the crossbar and none of the above apply, a goal should be awarded and the restart is a kick-off for the defenders.
It is currently allowed. So... now.
behind own goal line courtesy of a kick or touch by a team mate, a free kick from the corner would be awarded to the other side, that free kick is called the corner kick