That's one of the main gripes I have about the Template editor, Taglist editor, Macro editor, etc.
I use the main editor window to create my templates, then copy/paste the entire thing into the "Content" area of the Modify Templates dialog box.
Personally, I think that IDM should be using the same editor box that we use for coding, and have it include line numbers at the left, and use the same window colors / syntax highlighting when creating templates. But that's me (and probably quite a few others.) Better yet, it would be better to have a "Save As Template" option for the main editor window. Instead of saving to a file, we should have the option to save what we're working on as a Template, Macro, etc. When saving as a template, it should provide a dialog prompting for the template name, and a set of radio buttons to select whether global, environment, or language specific. If environment or language specific, then a drop down should be enabled to allow us to select which environment or which language to save it to. It wouldn't be that hard.
The Modify Templates should be changed to list the drop down for the Template Group (as it does not), and have a list of the Templates. There should be an "edit template" button, and the Content area should be a "preview only" area to allow you to see if you have the right one before hitting the edit button. The edit button should then place the template in the main editing window of UE for editing. When you hit save from UE, it should know where it goes just as if it were a regular file.
This will take some serious redesign, but I think it would really benefit a great number of people, and make the Smart Templates even better.
I'll send a feature request by email.