There is a lot of information here, and I am not an expert on teachers plans, but hopefully someone else will jump in. I am also assuming these are related to a defined benefit plan (monthly lifetime benefit) and not a defined contribution plan (pool of money)
Teachers plans are generally operated by the state and therefore some of the QDRO rules apply differently.
That said, to answer you basic question of "can a QDRO be amended post-divorce?", Yes, but it would be very rare. In order for the QDRO to exist, both parties had to agree to the current wording. Therefore, in order to change it, both parties would need to agree that the wording was now incorrect for some reason, they would need to agree to get the attorneys involved, then they would need to go back to court and get a judge to agree. So I won't say it isn't possible, but I have never seen it done.
I am also not clear what you would want to change. You mention naming children as beneficiaries, but that would likely not be possible even if you could change it. QDROs can only allocate the benefit the plan was obligated to pay. Generally, pension plans only pay lifetime benefits to the employee and their spouse.