Data Designer has been recently enhanced with a new capability called Cascade Add, in both SFDC and NXT editions. This functionality allows admins to add a field to a dataset, and thereafter this field automatically gets added to all of the next datasets (end tasks) in that design. Prior 6.19 release, whenever admins wanted to add a new field to the end task (dataset), they manually added that specific field to all of the tasks (including Merge and Transform datasets) in that design.
If you wish to learn more, following are the doc resources:
Happy Posting!