If I use the Opposed_Pair command on two stats in my stats screen, will I still always have to change both the stats, or can I just change one stat and the other changes automatically?
That’s not how opposed pair works.
You effectively use only one variable, the opposed pair is deduced from that only for display.
Let´s say you want to have the pair Coward/Brave. You’ll choose onlly one of these two to represent the pair in the code. Let’s say you choose Brave. So, this will be the reference. Every time the player takes a brave action, increases Brave, every time they choose a coward action, decrease Brave, etc.
Then on the stats page:
*stat_chart opposed_pair Brave Coward
Coward is there only for show, you don’t need a variable for it.
Take a look at the wiki page.
Specifically, Coward will always be equal to the difference between 100 and Brave.