Quick answer: Once per game, a team can choose any hitter to take a plate appearance even if that player is not next in the normal batting order.
Why the Golden Batter exists
It creates one deliberately high-leverage matchup. A team can choose the hitter it trusts most for the situation instead of waiting for the lineup to turn over.
Does it permanently change the batting order?
The Golden Batter is a special one-time choice rather than a complete rewrite of the lineup for the rest of the game.
For the full context, read the 11 Banana Ball rules.