One way only
As far as I can see there isn't a way of Trump undoing this. The President has the ability to commute a sentence (or grant a pardon - and yes, even in cases where no charges have yet been brought), but he doesn't have the power to extend a sentence or to impose one. That resides with the courts.
Even if it was possible legally, there is the political reality that no President would really want to mess with one of the few absolute powers of the Presidency. After all, if Trump does it to Obama, what's to stop Kang* doing it to Trump?
* Although to be fair, President Kang will have other priorities**
** Like building a death ray to destroy a planet we haven't heard of***
*** Don't blame me, I voted for Kodos.