I'm still not 100% sure I understand, but it sounds like what you want is to stop Bob reassigning the issue to someone else.
Have a look at the permission scheme - you need to modify it in a way that says "Bob is not included in the people who can assign issues in this project"
I have multiple projects that use variations of the same base workflow. The variations depend on the requirements of the project or issue type. The variations mostly come in the form of new statuses ...
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