If you're messing with ACLs I'm not sure deduplication will help you much; I believe (not much experience with reflinks) the dedup checksum will include the metadata, so changing ACLs might ruin any benefit. Even if you don't change the ACLs, as soon as somebody updates a game, it's checksum will change and won't converge back when everyone else updates.
Even hardlinks preserve the ACL... Maybe symlinks to the folder containing the game's data, then the symlinks could have different ACLs?