Dreed, I have to laugh because I have been going thru the same thing as you today. What I found is that its easiest to work the watermark from within the Print module. Also, like you, I found it very cumbersome to save changes but there is a way!
Open your image in the print module. Go to Edit/Watermark. The Watermark dialog opens. On the upper left corner, your saved Marks are displayed. Choose the one you want to edit. After you make your changes, DO NOT click save. Instead, go back to the drop down list where your original saved Mark was selected. Left click on it. You will get a bunch of options. On is UPDATE WATERMARK or something similar. You dont even have to open the save dialog. In fact, the way it presents is kind of confusing. If the save dialog opens, click cancel because you are not in the right place to "update". am not at my photo computer. If this does not work, post and I'll look after these storms blow by.
Paul