Ah, you’re right of course. My suggestion is only possible in the new version. Instead you should do something that works in both versions. Make a variable of the type Grid_Manager_Class and set its default value to Grid_Manager. Put it in your event graph, drag out its pin and get all actors of class. From the array you then get, get element 0 and cast it to Grid_Manager. For an example see the constriction script of Tile_parent.
If I knew Unreal was to upload the new version in a couple of days I guess it would make sense to wait, but since they still haven’t uploaded the version I sent them two weeks ago I wouldn’t hold my breath. Converting your additions shouldn’t take too long in any case. I recommend putting a new, unused variable get at all places you make changes so you can easily find them again by searching for the variable.