Trust terms vs. IRA designated beneficiary?

yes, it's legal, BUT ...

the IRA custodian can not be successfully sued for turning the IRA assets over to the beneficiary it has been told about instead of the Trust/Estate -- because it was not officially notified [official notification is changing the beneficiary -- which wan't done].

if the legal action of the IRA custodian in turning over the IRA assets to the designated beneficiary results in that beneficiary receiving an excessive portion of the assets, the other heirs, and/or the creditors of the estate, can not successfully sue either. [the deceased had the opportunity to change the beneficiary and did not do so, which effectively makes the actual outcome the choice of the deceased.]

also, the beneficiary of the IRA can not be successfully sued to force disgorgement of the IRA assets by anyone, since Congress intentionally set up the IRAs to be exempt, EXCEPT that excess contributions to the IRA may be fished back by the Estate/Trust, AND that transfers in bankruptcy [if the deceased was effectively bankrupt] may also be clawed back.

Lots of opportunity for law suits if there are insufficient assets to pay the estate's bills and debts ... which is why [in that case] the Executor should hire an attorney to help sort out the mess [and rebuff the claims of creditors to assets they have no legal right to seize].

Stop asking this and consult a lawyer.

Yes it is.