To lock a line number

On the ribbon, click Home tab Project panel Data Manager.
In the Data Manager, in the drop-down list, click Current Project Data.
If the current drawing contains the line number, you can use Current Drawing Data instead.

Note:
Exclusive project access is required to lock the line number. Locking a line number can modify more than one project drawing.
In the tree view, expand Area. Click Pipe Lines.
Right-click the line number that you want to lock (for example: 101). Click Lock Line.