Solved
To resolve we created a org level group named NWL_ECN_TEMPLATE_MODIFY and applied the below ACL's to this group:
ECN soft type: Read, Download, Modify, Modify Content, and Modify Identity
Change Activity soft type: Read, Download, Modify, Modify Content, and Modify Identity, Delete, and Create.
These changes were deployed only to dev platform. Now members of group can update the ECN templates on dev and then are moved to prod following validation.
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