It is not exactly a "clone": you just define a new UCM project, with at least one Strea, called by default an "integration Stream".
However, in your case, you could for your new parallel development (ie your new UCM project), use only that one "Integration" stream, in which case it wouldn't play really the role of "integrating", but would be a "development" stream.
That wouldn't prevent you, in this new parallel development project, to recreate whatever hierarchy of Stream you would need.
Each UCM project has always at least one Stream. Then it is up to you to create sub-streams as needed.
You would rebase that first empty Stream with the baseline of your choice (put on one of the Stream of the first project)
For keeping both projects in sync, you would deliver from one project to the other.
You need though to set the deliver policy "allow interproject deliver to project or stream
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