Change a property of a property of a class

[ehemmete]

I am trying to change the size of the presenter notes in a bunch of keynote files.
What I have been trying to do is set the size property of the text of the notes property of the slide class.
Here are the two things I have tried:
Setting it directly

tell application "Keynote"
	tell slideshow 1
		repeat with x in every slide
			tell x
				set size of text of notes to 9
			end tell
		end repeat
	end tell
end tell

This gives an error:

error “Keynote got an error: Can’t make every text of notes of item 1 of every slide of slideshow 1 into type reference.” number -1700 from every text of notes of item 1 of every slide of slideshow 1 to reference

The other attempt is to try to get the notes out, make the change, and then set the notes back

tell application "Keynote"
	tell slideshow 1
		repeat with x in every slide
			tell x
				set oldNotes to notes
				set size of text of oldNotes to 9
				set notes to oldNotes
			end tell
		end repeat
	end tell
end tell

Which gives this error:

error “Can’t set size of "This is a note" to 9.” number -10006 from size of “This is a note”

“This is a note” is the value of the note in my test presentation.

Any idea/help would be greatly appreciated!