Can real estate property already in an irrevocable trust be changed to name a new owner?

It depends upon whether trust provides to your mother a lifetime and/or testamentary "power of appointment" to "appoint" the house to one or more beneficiaries other than the person(s) who would presently receive the home under the terms of the trust. A power of appointment, if included in the trust instrument, must be exercised as provided in the instrument, or as otherwise authorized under state law.