Can the beneficiaries of an irrevocable trust be changed by petition?

The original trust was written as irrevocable with the beneficiary being my grandmother and upon her death the benefits were to be paid to her descendents "per stirpes." A petition filed in 2007 to appoint a new trustee included this language, "The inclusion of "per stirpes" in section SECOND with respect to a class that involves multiple generations ("then living descendants") is a curious use of the term. In the absence of anything in the trust to the contrary, the Petitioner's construe it to mean that upon ** death, all of her then living descendants are entitled to an equal share of the then remaining trust property, if any, and that the use of "per stirpes" without reference to a distinct class upon which to base representational distribution is meaningless." Does per stirpes apply