If you rename the custom PF1020.xml to PF1020.xml.add, let it remain in the Aoc\Yorgomir WP\Waypoints folder. Edit your waypoint file and remove the top 3 lines, down to and including the <Root> tag. Then scroll to the bottom of the file and remove the end </Root> tag. In short, your custom waypoints file should not contain the <Root> tags or anything outside these.
Then it will be added to the existing PF1020.xml file, with the content of your PF1020.xml just above the end </Root> tag of the original PF1020. Here is a link to your
PF1020.xml as it needs to be changed for this approach to work.