I don't believe you can change mid tourney regular season. those 3 are playing as individuals not as part of the team. If that was the case everybody would bring 8 instead of 5 and just rotate who was hot. this has been discussed in the past and you can do it to some level I believe in the championship. There are hurdles due to rankings and what qualifies players for the end of the year graduations to pro golf. if the ruled changed it was very recent.
Any of the bottom three in for Goeke and we gain a min of 4 strokes and a max of 15 for the tourney. But this isn't in a vacuum, when you are in the counting spots the pressure is higher for sure.