Ok, here is the method to use -
Look in your Templates folder and find the template you want to modify - it has a '.catx' extension.
Rename the file with an extension of '.zip' and unzip the files to a new folder. (Yes, the catx file is a zip file).
Now, in your new folder, look for the CAL folder and open the content.xml file with Notepad.
Look for the DAYFORMAT tag in the lower part of the file.
Now look for the CalendarText tag under DAYFORMAT.
For my Calendar I removed the font="bold", added HorizontalAlignment="Right" and VerticalAlignment="Bottom", changed the point size to 32.
Save the content.xml file (it may be Read Only so change the properties to Save it).
ZIP all files in your new folder to Template_Name.zip and then rename it Template_Name.catx
I was working with the Month calendar "Month_2ColDaySideBySide.catx"
Copy the modified file to your Template folder, open Calendar Print Assistant and look at your changes.
Good luck -