HOWTO/Change Creator Types on the command line in Mac OS X

Blatantly snarfed from a post by Nicholas Riley on the macosx-admin mailing-list:

/Developer/Tools/SetFile -c <creator code>.

To find (an app's) creator code the simplest method I know of is to use launch (or use 'fink install launch' if you have Fink). It gives you a result like this:

% launch -f /System/Library/CoreServices/Help\ Viewer.app
/System/Library/CoreServices/Help Viewer.app: scriptable Mac OS X application package
        type: 'APPL'    creator: 'hbwr'
        bundle ID: com.apple.helpviewer
        kind: Application
[...]

The Finder actually uses a slightly different method, but this one is much more space-efficient.

% touch blah.html
% /Developer/Tools/SetFile -c 'hbwr' blah.html
% launch blah.html

and you'll see blah.html open in Help Viewer.