The suggstions made in the link 'don't necessarily' solve the issue.
For mp3's there's 'some' players that'll change the icon to that of their own (eg: Audion & the audion os9 version is compatible with os8.6.)
The technical solution if the above suggestions don't work is to use a file utility. I use Mac Army Knife & use the File Attribute Editor to add the appropriate Creator & file Type codes (compare to ones you have.) You'd find that these are either blank or have LW as the creator. Changing them to what they should be & their appropriate icon will return & if you double-click them, the approp app will open them.