I noticed while looking through new hints that people have noted that some stationery options have display variations. Although the easy way noted in that hint only allows for a few adjustments (such as a color here or there), the stationery can easily be changed if you know how to to develop web pages.
All mail stationery files are self-enclosed web pages, much like a package file. Here's how to create your own.
- Create your desired stationery using your favorite web development tool.
- Locate the section of your stationery you would like to be able to adjust when in Mail.app, and enclose it with a span tag, with the following options:
<span contenteditable="true" apple-content-name="body" style="display;block;" - Move all items needed for the page (html files and images) into a new folder called Resources.
- Using your favorite plist editor, create a new plist called Description.plist in that same Resources folder. Add a string called HTML File and set the value to content.html. Add the following additional strings: Display Name, Folder Name, Thumbnail Image, and stationery ID. The values for everything thing but stationery ID should be self-explanatory. In the stationery ID string, enter a value based on this "72A27F00-FF50-43E8-A304-B2F85Ere89tfb" but it should not be exactly the same this is only an example.
- Add an Array called Images, and in it, place string entries titled 0 through nn, where nn is the total number of images in your HTML file minus one. For the value of each string, list the file name of your image; the order doesnt matter.
- If you are using a background image, create an additional array titled Background Images and list your background images the same way you did in the last step. Background images must also be listed in the Images array from the prior step.
- Save your plist file.
- Create a new folder and place your Resources folder inside of it. Name your new folder mytemplate.mailstationery, where mytemplate is the name of your stationery.
- Double-click your stationery file, and you will be asked if you would like to install the stationery
[robg adds: For the stationery ID entry, you can use uuidgen in Terminal to create a guaranteed unique identifier string.]

