As far as I know on a hypervisor system, a new partitioning can only be forced by reinstalling the entire system using a USB installation stick. Therefore, the size of a user partition cannot be changed on a hypervisor system without reinstalling the entire system.
It looks like you got some good answers from Corne and Jaroslav, and it has been a couple of weeks since the last activity on this post. If the answers helped you with your question, can you help the next person with the same question by marking the solution on the information which helped you the most? If you still have open questions on this topic, can you provide an update?