Rails - Mar 2006 - file_column: post processing to add or delete thumbnail sizes

Dear all,

I have been using file_column for sometime now, and have several  
pictures which have all been uploaded by file_column. Now, I would  
like to add more thumbnail sizes for various different purposes --  
and perhaps to even delete the sizes I no longer use. Is there a way  
to do this using file_column automatically? Or can someone please  
point me out to a script or a hint on writing a script which would  
take care of this for me.

Thank you,

Sharkie