I've got a Sharepoint site collection with several sub sites each having their own document library. Now I want to add the file extensions to the document names in all those libraries. How should I do this?

I've seen tips telling you to modify the onet.xml-file, but they never look like mine do, and furthermore I don't know for sure what happens to that onet.xml-file - does it change the existing libraries? Other tips tell me to use Sharepoint designer, that would mean I'll have to do it for every view in every library, wouldn't it? So I'd prefer doing it from code, where I feel more comfortable and where I can automate the process.

So, all I want is to replace the "Name (linked to document with edit menu)" with the "Name (for use in forms)" but still keep the link and the edit menu. I've found I need to use the FileLeafRef-field, but I don't know how!

Thankful for any new clues, Sebastian