Ubuntu 12.04 Unity - Easy way to open a file in GUI text editor

I'm a new Ubuntu 12.04 Unity user coming from a Windows background.  One thing I do a lot in Windows is rename the extension of a file so that Windows uses a different application. For example, I change the extension to .txt so that clicking opens the file in notepad or wordpad, later renaming the extension back to resume using my "normal" application associated with that extension.  If only doing this "one time", instead of renaming I would right click and specify the application from the context menu.

With my short experience under Ubuntu, it seems that the file extension trick is not applicable. Also, on some files (like svg) the context menu does have an "Open with" option but other files don't.  I find myself going into terminal and using vi which takes longer for me.  Is there an easy way to open a file in the GUI with a different application (assuming the context menu lacks and "Open With" option)?  I'm hoping for a technique that makes it quick and easy to modify the application that is used to open a specific file, even if just for one time.