Is it possible to change the % time allocation of a user on a per sprint basis?

For example, we have a person that belongs to 2 teams. For the first few sprints in a release they will be 30/70 allocation. During the third sprint, they will be more 50/50 allocation across those same two teams.

It doesn't seem like this type of resource planning is enabled in 2.0.0.2. If that is truly the case, are there any recommended ways to achieve this?

Should we just update the Work Assignments for that user when they shift over or should we do something more advanced w/ the way we setup teams and Project Timelines?