MindMyMinistry supports a feature called song tagging, which is a fancy way to arbitrarily organise each of your songs into multiple lists. This is done by assigning one or more "tags" to each song.
In the song detail screen (you can get to this by going into Songs, and then clicking Edit on any one of your songs), you will see the Tags field:
Simply type the keywords you want to add to the song and MindMyMinistry will create tags for them.
Once saved, the Songs screen will let you search by tagged songs by simply selecting a tag from the box:
