Here is a discussion from a while back where I explained how to change all the notes font and font size at once. Make sure you read it carefully (especially the part about making a backup before starting any document surgery). Below is how to get to the files if you don't get the option to Show Package Content.
I don't usually use presenter notes so I am not sure why this happens. You can go to the Keynote Menu>Provide Keynote Feedback to tell Apple what control you would like over Presenter Notes and then wait and see if it gets implemented.
If you don't have the option to Show Package Content, follow these steps
Go to the Finder and find your Keynote file and make sure that it has the .key extension on it. If it doesn't, click it and command i to view info and uncheck the box that says Hide Extension.
Delete the .key and change to .zip and then click the use .zip in the dialog box that comes up
Double click the new .zip file and it will change it to a folder
Open the folder and see the files that make up the Keynote
Close the folder and add .key to the end of the name and click Add in the dialog box (this will change it back to a Keynote file)
Printing is buggy. When you print from Keynote, a bug resets most or all presenter notes to Helvetica 12 and grays them out, preventing any changes in the notes (slides are unaffected). The same goes for saving to PDF, which the Mac interprets as printing.
So when you print any Keynote slides with presenter notes, do this: Save file > Print > Close (without saving) > Reopen.
Apple engineers duplicated the problem the other day and have put it on their to-fix list . . . or so I was told by the nice man at Apple Support.