If somehow a team figures out how to do this will this be legal? I am talking about if a red alliance robot scores a barrel first in the goal, and then a blue alliance robot lifts the red alliance barrel, and places a blue alliance barrel. I know you are not allowed to descore but it doesn’t descore it simply lifts the opponents game object up to place one of ours.
No, this would not be legal, as per the updated version of <SG9>. Once a Bonus Point is earned under Clause 1 of the definition of Scored, it cannot be changed. A similar question was answered here, where you can find a full quotation of the rule: