There are a few ways I can think of to manage your scenario. I'll outline them below, but if others have suggestions, we'd love to hear them!
Option 1: Using the Uplift Feature
You had noted you found information about Uplfit, but that option can also be used to manage price changes going the other way.
This is an example of how Uplift would work:
Your product is set up with a base price of $300.
When you create your subscription in Salesforce via a Quote, you can override the pricing at this point and set it to $480.00 for the first year's term, assuming your terms are 12 months long.
At this time, you will want to also make sure you are setting your Price Change Option when you select your quote to "Use Latest Catalog Pricing"
When the subscription renews, it will pick up the latest catalog pricing -- which should be at the $300 price.
Option 2: Creating an Update Product Amendment
This option doesn't make use of the Uplift feature. Instead, it will rely on an amendment to manage the pricing.
You could create Quote for $480.00 and create the subscription when you send over to Z-Billing
Then you would create an Amendment Quote with an effective date set to the first day of next year's term and the pricing at $300.00
Doing this essentially set everything up in advance for you so when the renewal happens, it will take the updated pricing.
... View more