I am aware this idea has been posted some years ago already, but unfortunately closed. I give it a new try!
Shelving changesets can be very helpfull! I know Microsoft TFS supports this for some years already.
You've been working on a problem for a couple of hours, but just can't find a solution for now. You've made a lot of changes locally that you don't want to lose, but for now, it's better to move on to another issue.
In this case, you do not want to commit your changes, but you don't want to reverse them either! Here shelving comes in: put the changes 'on a shelve'. They do not hurt anybody, they are just for yourself.
One shelved, you're changelist is empty and you can work on fixing the next issue.
Axels workaround could be done a bit easier: not need to close the project, just download it again, the project will be closed automatically. renaming can be done after you've downloaded the project.
The alternatvies of Bas en Axel do help out, but still it would be better to be able to shelve the changes. You got my vote!
Maybe you could create a new branch when you start working on an issue
A workaround: close the project in the Modeler, rename the project folder (add a prefix), and download the project again from the Team Server. Your local changes are still in the project in the renamed folder and can be altered and committed later (after updating).