In the UMG editor the “Is Variable” check box doesn’t seem to do anything if you have multiple objects selected.
Pretty easy to test, just create a new UMG widget, add something (it can be anything) to the default canvas panel, select both the canvas panel and the new item, and click the “Is Variable” check box in the details panel. Nothing happens, you can verify by selecting each individual item and seeing that they haven’t changed from the default.
Would be nice to be able to change this property on multiple widgets at once instead of having to do it on each thing individually.