I believe you're talking about the Default tool in an file's icon.
The way I deal with this is by not saving icons with files and using DOpus Magellen II filetypes to attach an appropriate icon. All I need to do then is change the Default tool of the 'master' icon of a particular filetype, and all iconless files matching that filetype will now have the new Default tool.
If you don't have DOpus there is a program called DefIcons which IIRC does a similar thing. I believe it comes with OS3.9 and is also available in an earlier version on Aminet.
This only works on iconless files (viewed with Show All from one of the WB menus), you'll have to set up your programs (i.e. Wordworth) to save files without icons. I'm not aware of any program that can do a batch operation of this sort on existing icons.
I recommend going for the no icons approach though. Saves heaps of HD space and makes file handling much easier.
