Hi @JH-W ,
Yes, it's possible to delete the content templates, content blocks etc using query activity and Update data activity. For example to delete content templates do the following:
Create a workflow then on
Query activity: set the Resource to content template and using the content template attributes available defined the target (you can date ranges as well).
Update data activity: Select the operation type as "delete" and under identification tab select the "Directly using the targeting dimension" as "Content template".
This will delete the content templates for the criteria defined on query activity.
Thanks!