I do not know what diagramming means, but, I, as an incompetent twit, wish to make a tentative attempt at determining the function of "accustomed to". Why attempting? I like to see my nonsense in print. It is one of my caracter faults, please forgive me.
I think a "that/which were" is missing from the sentence. The words have been wiped out via a means of a grammatical method called ... um ... I have no idea.
Somehow I feel the "accustomed to" belong together.
This is merely an intuition for which I can't find any irrefutable base. I am a bit reluctant to believe accustomed is adjectival. I think it has more verbal force than it has adjectival one. Again, intuitions.
I am not a teacher, please wait for a creditable answer from a trusthworty member. I am not one.