It is possible to lock data selection lines. this prevents them being deleted and being changed.
In the version design, select the data selection line, then right click and select "advanced", then check the Locked checkbox that appears.
On some tools releases, this "locking" is lost when the version is checked in - however, if you make a data selection design change at the same time, the "locking" takes effect.
Matthew
E1 8.10, 8.97.1.2, Oracle 9i, Solaris