Hi,
The full feature set IAP available in Cubasis LE updates the app to the similar feature set of the Cubasis Full version.
However, the app icon and name will remain Cubasis LE. The additional in-app purchases (like Classic Machines, FX Packs) are also bound to the app version, in which these have been purchased. Additionally, Apple does not offer upgrade options or other discounts, when changing from one app to another app or similar.
Hope that helps to answer your question.
Best,
Lars