I don't think WotC gave Larian a blanket permission, because it would be unusual for a corporation their size to be that "freestyle" about their product development. WotC might not have a detailed plan on every change, but I'd expect they have a corporate strategy defining the direction they want to take in the computer gaming market with their various products.
I agree with you. WotC wouldn't give blanket permission to make any change Larian wants. But as you brought up, it's a bit unreasonable for Larian to get WotC's permission for every single change. Larian can probably freely make "changes of this scale"=small scale changes
Height Advantage: The DM is allowed RAW to give Advantage on anything reasonable = no need for WotC's approval Surfaces: Are technically a thing in D&D 5e (alchemist's fire, various spells) = no need for WotC's approval Concentration spells while wildshaped = Honestly this might (hopefully) just be an oversight on Larian's part that will be corrected Action changes to disnengage/hide/etc is probably the only item on my list that really needed WotC's explicit approval