I know I can change file association by right click at file -> Properties and there are a space to change this. But I can have an utility with a list of applications where I can do this to all file types and extensions, and where I can add new extensions and associations. It's more simple to work. KDE4 have something like this on "systemsettings" utility, at submenu "File Associations" (KDE3 have too, but in KDE4 it's best).