[Custom Feature Question] How do I make a trainer use their Pokemon in order?

Normal trainers can use their Pokemon out of order and it's fine, but trainers like gym leaders, the team admins/bosses and the elite 4 should use their Pokemon in order, especially if they have an ace Pokemon who should be used last. However, trainers tend to pick the Pokemon that fits the situation best, which isn't always a good thing.

How can I make a trainer use their first Pokemon defined to the last one in order? Thanks in advance!

I'm pretty sure that there's a thread about this somewhere here. At least that's the case according to a RC thread.

We have this too (like a switch):

https://www.pokecommunity.com/showthread.php?t=339568

It appears to have worked! Thanks for your help!