This seems to be two differnet (and unrelated) questions…
Blynk do plan to re-introduce projects…
Projects obviously require multiple devices, which is why I find the mention of a single device slightly odd in this context.
When you update a project in the web browser the changes are updated to the app too (assuming that you choose that option).
Obviously if the changes require different functionality in the code then a new sketch would need to be uploaded. Whether this would overwrite your dynamically provisioned credentials depends on the type of board you are using and what options you choose when you compile the BIN file i guess.
But, if it’s an issue then you don’t have to use dynamic provisioning if you don’t want to.
Pete.