I would say that the term ‘unlikely’ comes from the argument that adding additional constraints to a sequence_item to create a new test is unnecessary.
When you develop a base sequence_item, it is constrained to the entire valid state-space for that specific agent protocol. If your DUT will support only a sub-set of that protocol, then you will add additional DUT specific constraints, and this sequence_item will be used in all of the test sequences for your DUT.
Ideally, you will always want to generate the widest variation of sequence items for testing. If you override your sequence_item with even more constraints to simply generate a new test, you are limiting the effectiveness of these tests.