I am using Greenshot 1.2.10 and unfortunately couldn’t manage to restore pictures with added elements to update/change elements after reopening. Possible to mention how this can be done. Somehow I would expect that this feature has been implemented already with 1.1. like reported by FEATURE-290, wasn’t it?
Unfortunately it's not possible to do this with files created in older versions.
But you should be able to store a Screenshot with annotations from the editor via "save as" using the Greenshot format. This can be opened again to continue working on it.