I don't know if this helps but, I've tried the new feature with your mod merged with Extended Timeline and so far I haven't got any problems. The provinces change their goods without problem. It works fine.
I have a few suggestions (I don't know if they can be done or if you like them, it's up to you, they are just suggestions):

1- What if instead of changing the good to any other you already have in another province, change the trade good to another one that has possibility to spawn in that province? For example: A province "A" has the chance of getting fur, naval supplies and fish. I colonize it and get fish. What if instead of letting me set the trade good as any other good that I have, it just gives me the option to choose fur or naval supplies. I think this way the feature wouldn't be OP. Or maybe you have another intention with the feature. Anyway it's just my point of view.
2-What if the cost of the change appears in the building menu and not in the event?
3-Maybe different prices? Maybe the cheaper trade goods are cheaper to change to than the expensive ones.

1- Well i have a big problem with balancing this feature because i don't want situations where you spam high price trade goods
2 - building menu is to smal for 67 trade goods
3- already in

You should nerf the Prodution Leader modifier of Copper since it's easily to get and the +15% Artillery Combat Ability is way to rewarding you should nerf it to 5%-10% since there aren't many nations with Modifiers which only affect the Artillery

@Francuz, so what about locking the change trade good by Super Region, so if you change the trade good say in Paris you can't change a trade good in the France Region for the next say 40years, additionally to encourage strategic goods usage, debuff the goods produced for a certain duration this way you are encouraged to say change the good in a mountain province to soething that helps fort defense or copper in a overseas region to build armies faster to help with rebels but if you only want a small foothold that say has a strategic value (like Alexandria as it cuts of maghreb from egypt, has a fort and CoT) maybe go for Beer to reduce unrest

I'm not sure if this is me, or if this is a big thing for a lot of people, but Brass never seems to spawn in my games? I havent played to completion but Brass isn't available to be made from a building, and it never spawns naturally

question: why cheese and beer not get bonus from the soldiers households?

oh and also, is it possible to add a modifier for provinces you build one of the trade good buildings that just says "used to have x trade good"

Do colonial nations not share their special goods with you? For example, American colony has Tobacco, but I don't have an option to force import to myself so I can build a cigar factory. Is this intended? I am also using subjects expanded.