Gill, here is a picture of the Variocharger on the 9.20. Is that the same one you have?http://www.michelprattesport.com/com...uct/A30000.jpg
If yes, then no more warranty, but if you haven't had a problem so far, then you should be ok. The problem with redrilling this riser (and others in the Atomic line) is that every manufacturer has a different hole pattern and might be too close to the predrilled holes, or the riser mounting hardware. Another compatibility problem is that the Atomic risers are designed to flex, and the design of the Atomic binding allows the heel to float in its track. Using a non-floating binding, greater stresses are applied to the riser mounting hardware, and could cause failure. A physics thing.
If no, and the riser does not have predrilled holes, then your one year warranty has expired or will expire anyhow.