Thanks for the quick follow-up. Luckily, I have not made any cuts yet! I did install collar ties in the shed I built - just didn't equate them to the number of ceiling joists present in the home. I suppose that the joists that 'outline' the room would need to be reinforced, and a sturdy box be built at the top of the present walls.
I will consult with a structural engineer. I suppose that I can get advice/specs from one, then still plan to do the work myself.
Your responses have made me curious, and I will be climbing into my attic to look at the vaulted kitchen ceiling. Obviously, I would like to make sure IT was done correctly! We had the house inspected by a certified home inspector, and he did look at it - his only comment was about the insulation job - no structural comments.
Can I assume that he would have pointed out a potential problem in that area?