For whatever reason Open In... will only list 10 apps. Usually this is the first 10 you downloaded. If you have a lot of PDF style apps that you don't use, try deleting a few. You should be able to add them back later, once GoodReader starts appearing on the list again.
Also, if you don't see 10 apps, try scrolling down. There may be more that don't appear in the chooser window.
And to answer your question directly. No, there is no way to edit them. I don't think it occurred to Apple that people would download more than 10 apps for the same file types. Hopefully they've seen the errors of the ways and are working on some improvements.