Hi there @Oduah!
Don here from Shopify. :)
This isn't a question we can field from here at Shopify ourselves, but we should be able to point you in the right direction for support.
If you are wondering how Paystack will behave in a given circumstance the best place to ask about this would be with Paystack support.
Bear in mind that currency converter-type apps will not change the 'home currency' of your store which your customers will check out in.
If I were in your position I would reach out to Paystack once you have chosen the currency app you want to use so you can work with both them and the developers of that app so you get a clear picture of how they might work together in your store.
As with all third-party apps in our store, you can reach out to the developers directly with any support queries you have by using the contact details listed on the app store page.
All the best!