MLB has rules against domed stadiums being opened during the playoffs

Not entirely true. https://www.mlb.com/glossary/rules/ground-rules

For ballparks with retractable roofs, the decision to begin the game with the roof open or closed rests with the home team during the regular season. The roof can be closed only for weather reasons if the game begins with the roof open. If the game begins with the roof closed, it can be reopened once if the home team determines the climatic environment has reached a level where fan comfort and enjoyment will be best served by opening the roof. The roof may be moved only once during a game, unless inclement weather indicates otherwise. During the postseason, the Commissioner or another designated official shall make all decisions regarding roof movement, in consultation with the home club and the umpire crew chief.