Skyoptin Free Font Renamer is not an answer to the question. Here's what it says: "Got a font collection? Got a collection, but no order in it? Start by giving font files the names corresponding to the full font names. For example, you can rename MLON_I.TTF to Milion Italic.ttf." It's a Windows app that automatically renames the font files in a folder to match the internal font name. It doesn't change the internal font name.

I use Font Monster for Windows 3.1, in Windows XP in a virtual machine. It can change the font name, family name, and some other properties without changing the rest of the font. As a Windows 3.x application, it can't navigate folders or open fonts with more than 8 characters in the name (or 3 in the extension), but it's worth the effort. Unfortunately the vendor disappeared long ago, so you can't register the app and get the additional features of the registered version, but the unregistered version can change names and save files. I have not had any luck trying to run Font Monster in Wine in OS X.

I had four fonts that should have been in one family but were named so that regular and italic were in one family and the bold equivalents were in another. I used ttx to change the family names in the bold fonts but then Font Book complained that the POST table was unusable, don't use these fonts. So I fired up Windows XP in VirtualBox, started Font Monster, changed the file names and copied the files to an accessible folder, opened the files in Font Monster, changed the names (two places), saved the files, moved them back, renamed the files (not really necessary), installed the fonts, no complaints from Font Book.

Font Monster is available from Vetusware at http://vetusware.com/download/Font%20Monster%203.5/?id=10581