How to change "Open With" with force and fury?

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http://askubuntu.com – Every [too often] in a [forever] there will be problems with the Open With context menu item. I've seen it changed around a lot, and it's still horrible. Applauds Now once again I've got a corrupt item that I want to replace with the correct item that is installed cleanly into the Application menu. I updated a program, and although all traces of the old are gone, the context-menu insists on living in the past. I cannot for the love of me find a fix. What did I do? I installed the (awesome and overshadowing all the other excuses for image viewers for Linux out there) XnViewMP image viewer. Th (HowTos)