Yes, once the trust grantor becomes incapacitated or dies, his revocable trust is now irrevocable, meaning that generally the terms of the trust cannot be changed or revoked going forward. This is also true of trusts established by the grantor with the intention that they be irrevocable from the start.
However, certain estate planning techniques allow for Trustees and trust beneficiaries to modify and redirect trust assets even in the instance of an irrevocable trust. One common planning tool is the use of a power of appointment, which allows the trust beneficiary to redirect their interest in a trust to a specified pool of remainder beneficiaries (including individuals, trusts, organizations, etc.). This strategy is helpful in a variety of situations; for instance, allowing a trust beneficiary to exercise a power of appointment in favor of a special needs trust for a grandchild who was not then living or disabled when the grantor created the trust.
As of January 1, 2015, the Maryland code allows for modification of an irrevocable trust by a court, if such modification would better conform to the grantor’s intentions. Likewise, a trust may be terminated by a court (or without court approval if it holds less than $100,000) if termination will not defeat a material purpose of the trust. Moreover, if you have found yourself as Trustee of a trust created out-of-state that may need revisions, decanting—or pouring the assets over to a trust with corrected terms that accomplish the same ends—may be a possibility.
A seasoned estate and trust attorney will be able to assist you in determining whether revisions to a specific irrevocable trust are possible, and if so, can help you select and implement the best technique.