how do I apply the changes I make in one slide regarding presenter notes to ALL of the other slides?
The default text in notes cant be changed as of 6.1
The has to be done page by page:
Use the following keyboard commands to copy the formatting you want and then to paste the formatting to other text.
select the text you want to use then to copy the formatting: option command C
select the text you want to format, then to apply the format: option command V
Using Keynote 6.2.2 or 6.5 create a paragraph style for the text in presenter notes:
change the text then click the + button and give it a name
then save the presentation aa a theme
when you want to change the presenter notes, type in the text then select the new theme and then change the text using the new paragraph style