You can't edit the Open With list, it is created by the system by polling all your installed applications for their list of files that they can open. If a program claims it can open jpegs, it is added to the list. If it lacks a notification file for the system to read it won't be added. There is nothing you can do about either situation--you can't add, subtract nor rearrange the list.
The absolute easiest way to occasionally open a file with some program other than the default is to launch the program, then drag 'n drop the file onto the icon of the running program in the Dock.
If this is something you do semi-regularly you might want to make a new Service using Automator to open a selected file with your program. Thus I mainly want my html files to open in Safari when double clicked, but since I hand code I ofter want to open the file in both Safari and TextEdit. So I made a Service to open in TextEdit. When I right click a file there is my Service down at the bottom of the Contextual Menu to open the file in TextEdit.
Rob Griffiths has written a tutorial on creating a Service in Automator:
http://www.computerworld.com/s/article/9137494/Howto_create_a_Service_in_Snow_Leopard?source=rssnews
There's an introduction to Automator here:
http://www.macosxautomation.com/automator/transcript.html
Personally I really like the "new" Services and revamped Automator.
Francine
Francine
Schwieder