How do you do that? because I cannot understand how from the .guide that comes with DefIcon. It would be helpfull for me if I could somewhere define a rule that all .jpg or .guide are always opened with some specific tool!
So there isn't a version where you can actually determine which icon to associate with which file?
Yeah, you can do exactly what you are asking for. Go to Prefs/DefIcons. Just open DefIcons and look for the filetype you want. (If it's not there you can add new filetypes) Using Jpeg for example. Just select JPEG, right click and choose Information, the default tool is what you want to change. It's probably set to Mutliview.
Now, any jpg file (that doesn't have it's own .info file) will open with the program you selected.
Deficons works on the MIME types embedded in the files. So unlike windows it doesn't matter if your JPG actually ends in ".jpg" If you have a file named waterfall.jpg and renamed it to waterfall.mp3, or just waterfall, it won't matter it will still open it as a jpg.
Now if your .jpg has it's own .info file, it will open with whatever program that .info files specifies.