Shooter for pregame technical foul shots

[splitveer]

Pre-game warm-up; player dunks at the 12 minute mark. Coach was informed of the player and that he would lose his coaching box.
10 minute mark; official book is checked and approved.
Start of game; coach of the team who is shooting free-throws wants a substitute to shoot the technical foul shots.
I understand anyone can shoot a technical foul.

Can you substitute for a starter other than for injury before the game starts?? And if so, does the substitute have to stay in and start the game instead of the original starter.