If a spell or ability’s targets are changed, or if a copy of a spell or ability is put onto the stack and has new targets chosen, it doesn’t have to target a Flagbearer.

Flagbearer is a creature type, but while you control Enroll in the Coalition, you’re not a creature. You can’t be the target of spell or abilities that target creatures but not players, even if those spells or abilities affect Flagbearers specifically.

If a player chooses targets for another player’s spell or ability, or if targets are chosen randomly, they don’t have to target a Flagbearer.

Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keywords are activated abilities and will have colons in their reminder text. Triggered abilities (written with “when,” “whenever,” or “at”) don’t have to target a Flagbearer.

Any player’s Flagbearer may be targeted. For example, if each player controls a Coalition Honor Guard and you control Enroll in the Coalition, an opponent’s Shock could target either creature or you, but not another player.