Ukulele chord diagrams

I found in a thread "Ukulele Chords_gcea.mpal" and successfully loaded it into MuseScore. Great Thanks to whoever created this file! I have attached it to this post so others might find it.

It isn't clear to me yet how to properly add these into my score, but I assume I select a note and drag a diagram to that note.

Instead of adding a chord diagram above notes in the score though, I would like to create a "catalog of chords used in this score" near the top of the score. Do I need to create some sort of box in which the diagrams can be placed?

Finally, should I need to, how do I go about editing these diagrams, or adding one to the palette?