No, the successor trustee probably is not allowed to alter the trust. Technically, it depends on the trust document, but that would be very very odd for a trust to allow that. If the trustee is uncooperative, consider finding an attorney to write a demand letter to the trustee. Demand letters from a law office often scare people into doing the right thing. If that doesn't work, you my need to hire a lawyer to sue to get the trustee removed from office.
Generally I don't offer my personal services in these types of forums, but this is an area of law in which my firm excels. If you can't work it out yourselves, feel free to contact me, Jared Richards -(702) 436-4333,
www.bdtlawyers.com. Around 30% to 40% of my career has been in litigation involving trusts. Others in my firm also have significant trust litigation experience. Other qualified attorneys in town include Mark Solomon and Layne Rushforth (both at different firms). Naturally there are others as well. Make sure you find a firm that focuses a significant portion of its practice on trust litigation.
Good luck.
Jared Richards.