Hi Risman,
We do recommend that unstable versions should be used only for testing as features and changes that are part of these versions are still in progress. That being said, I believe these extensions and endpoints should be available in the next stable API release, 2023-10 available on October 1, 2023, so it could be worth testing out the Checkout Extensibility developer preview to see if it will achieve what you’re looking for.
Hope this helps!