Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Can subscriber Add actions to, or modify the actions of a workflow in an installed managed package?
Subscribers can add workflow actions but not modify existing actions or remove them.
Packaged workflows or field updates themselves cannot be edited with very few exceptions like Email Address. They can be deactivated though.
From the in-org help:
Required, but never shown