After creation of 2D drawings, the entire drawing act as a single entity including dimensions, levels, position flags etc and no any manual modification is allowed.
1. Go to Utilities > Named Groups. One new dialog box will open.
In CONNECT Edition Go to Modeling > Home > Groups or Drawing > Home > Groups and click on the right bottom button
In that you need to tick off the box in Selectable column. The drawing then be editable.
There is one more Wiki on this topic. Following is that Wiki Link:
https://communities.bentley.com/products/prostructures/w/structural_drafting_and_detailing__wiki/18263/prosteel-grouping-in-details-handling-under-microstation-named-groups
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Bentley LEARN Server