From KoakuCIG - @EmaltbyCIG

1. If a player has completed the Save Stanton as well as Phase 1 and Phase 2 of the Fight for Pyro event, their account is flagged and they receive rewards based on what they accomplished. Phase 3 is purely narrative and does not include any rewards, but does a flag get placed on the player’s account showing they participated in Phase 3? Nope, participating in Phase 3 doesn’t change or add anything
2. If a player chooses to skip Phase 3 and earn aUEC elsewhere will this be a detriment to their account flags or rewards at a later time? Nope, if you dont wanna play it you won’t loose out on anything in the future

The skins that have been awarded out and posted in this FAQ are the only skins for this event