Nevermind!

Had to jump through some hoops, but here's what I did.

1. Open upgraded project in Data Tools

2. Add Existing SSIS Package from old project

3. Go to Source Control Explorer window, right click package name, choose Undo Pending Changes. (This will keep the package name in the project's SSIS Package list but remove the package from the folder itself). EDIT -> If this doesn't work, start over and use Rollback

4. In Source Control Explorer window, go to old project, right click the package, and Branch to the new project folder.

5. In Source Control Explorer window, return to upgraded project folder, right click branched package and choose Check In. Enter comments and click Check In button.

6. Resolve Conflicts window will open up. Choose Overwrite Local File and Folder. The conflict will clear.

7. Pop back to Source Control Explorer Window and view the history of the package to see the previous history brought along with this package. (verification).

8. Complete package upgrade and check it back in.

YAY.