You can do all this yourself without bothering Glide Support.
You already have an answer to your question about swapping the URL’s.
As fas as the subscription goes, all you need to do is downgrade the plan on the currently published app, and a credit will be applied to your account. You can then upgrade the replacement app and that credit will be used towards the cost of the upgrade. It should be a cost-neutral exercise.
If you use the same URL for the replacement app, the change should be mostly transparent to your users.