I only use 5 1/2 x 8 1/2 paper for brief thank you notes on preprinted card
stock.

Currently - I open up a new document and using "page set-up" select 5 1/2 x
8 1/2 paper (easy to do)

Then I have to change the default margins that come up and select the right
paper tray. This is a real pain and I have to keep looking for the piece of
paper that I jotted down the margins on or try to remember where in Notes in
put same information. Mostly I just play around with the margins for the
100th time and wing it! Aaaaaargh!

How can I change the DEFAULT margins related to the 5 1/2 x 8 1/2 paper size
? Then they would come up the same everytime I wanted to send a thank you
note.