Alright, it wasn't mandated by the court but instead was based on an agreement between the two of you and became part of your division of marital assets. I have no need to check the site. The problem here for you is that while TRS may "allow" a TRO to set out a limitation, that has nothing to do with what you are able to do now, after the fact, when the agreement is already written in stone, so to speak.
As for what the TRS told you, I agree---anything can be stipulated to. And if allowed by the plan, you could limit the payment to a dollar limit as well----but that applies to new, negotiated agreements.
However, you already stipulated to an agreed amount, put no limitation on it and unless your ex now agrees to change that way of determining his share, then you are without a legal remedy.
The court does not have the power to force a modification of your settlement "contract" with your ex from the divorce
The straightforward answer to your question, "Can this be changed?" is no, it cannot be changed now---at least not without the full cooperation and consent of your ex; which I presume will not occur.
I understand that you may be disappointed by the Answer you received, as it was not particularly favorable to your situation. Had I been able to provide an Answer which might have given you a successful legal outcome, it would have been my pleasure to do so.
If you have additional questions, you may of course reply back to me and I will be happy to continue to assist you further until your questions have been answered to your satisfaction.
Kindly take a moment to rate my service to you based on the understanding of the law I provided. Please understand that I have no control over the how the law impacts your particular situation.