The answer by dpb is what you should do, but the answer to the question as posed is this:
Matlab is closed-source. Mathworks will probably not accept any changes to their code that they didn't write themselves. The cost is not just the edit itself, but also editing the documentation, added testing load to confirm no bugs are (re)introduced, and opportunity cost. The time spent on this function can't be spent elsewhere.
However, you can send an enhancement request which they may act on. It does happen, but they have to be convinced it is worth the cost.