Is there an easy way to mass change the data set on a series of cards?
If your seeking to change all the cards powered by a dataset to anhother one you can use Data Center / Datasets and in the dataset detail on the "Cards" separator you can choose "Switch cards to different Dataset"
Hope this helps.
not really wanting to change all the cards which are using the data set just a group of about 15
In that case i think you will have to go and edit each card manually.
This has been posted to the Ideas Exchange at https://dojo.domo.com/t5/Ideas-Exchange/Move-SELECTED-cards-to-a-new-dataset/idi-p/24604 to be able to move selected cards to a new dataset just as you select which cards are included in a presentation.
Well that's not very convenient.