I have an already-exists website with /api url. I'm testing a migration to IPB4. I cannot change our API entry point for existing customers.

I cannot override the /api url management in IPB4 via furl json files, because api/index.php file physically exists.
But if i rename the /api directory to /xx_api, nginx try_files don't find it and i can match it in my IPB custom application via normal furl management.

My question: IPS original /api is used internally somewhere? My workaround is safe or cause issues? 

Thx for any advice.

We do not internally reference /api/ anywhere in the software, except for with the API management area of the AdminCP. Generally speaking you should be fine to remove that folder (or rename it).