Would it be legal for me to make pen & ink changes to the names of executor and trustee in my existing last will & testament?

Once a Last Will and Testament has been signed and witnessed, under Massachusetts law it is too late to make changes directly on the document. A codicil or revised Will should be done afterwards to make any desired changes. Writtten changes made directly on an existing Will could result in expensive litigation about what was intended and whether the changes were effectively made.