will the tunze 9002 with the magnet attachment fit in the back of my biocube or do i have to saw off the magnet attachment or is the magnet attachment detachable?
It's normally detachable, at least the old model was. Does it look like it was glued onto the body? Please don't break your new skimmer because of my suggestions you could also tryout the steps below.
You don't "need" to make any adjustments, but you will find it very difficult to fit the 9002 low enough in the back chamber to get the right water height because the collection cup wont fit well. You could give it a try, I ended up cutting a part of the lip on the back of the aquarium to fit my skimmer. You could also pick up a new collection cup from: BioCube 29 - inTank, LLC