For Decals, you need to run Update From Libraries ...
OK... What about the other changes to the layout?
" I've made changes to decals, the board outline, copper planes, and the Constraint Manager."
Decals - describe above. While that sounds really weird, it works because even though there are no changes in the schematic, you still need to Forward Annotate with the 'update from Central Library' box checked to pull the updated decals out of the Central Library.
Board outline, copper planes - How do you make changes in Layout and have them not "immediately update in my layout"? That makes no sense. We'll need more specifics. It sounds like you forgot to save the file, or you were editing a copy and not the file linked to DxD. If you need to sync a new Layout file, open the Layout file first (before DxD) and connect it to the project. Then open the DxD project and all should be good.
Constraint Manager - I hit a bug similar to this in VX2.1 or VX2.2. You probably need to open a SR because I don't remember how it was resolved.