Gotcha. I’m pretty sure in the postseason tournaments you can do that. I think it started with allowing an injury substitution and they quickly realized that it would impossible to verify who was really injured and who the coach just wanted to sub out. Now all teams bring 6 and play 5 in the postseason. You are right that it would be an unfair advantage in this event where pretty much all the teams just bring 5.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.