Because each document in a Living Trust (i.e. the Trust itself, Durable Power of Attorney, Health Care Power of Attorney, Pour Over Will, HIPAA Agent, and Personal Representative documents, etc.) performs or provides a different service or function, preparing an amendment for each document would be most prudent.
The amendment would need to be executed in the same manner as the original; that is, if the original is witnessed and notarized, then the amendment should be witnessed and notarized.