Change a UTI's association with a particular file extension

[Melab]

I have file extensions associated with the UTI com.rarlab.rar-archive that I don't want. How can I change this? Doing "Change all" in File Info does not do it.

I'm running Mac OS X 10.5.8.

 

[Melab]

Did I make this question clear enough? I didn't then I can.

 

[Melab]

RCDefaultApp doesn't do what I need to do.