not for the viscous center diff, if you went with say an electronic center diff that is capable of going from full lock to full open that would work, or if you go with a clutch type center diff where you can reconfigure the plates to allow the power all to the rear.

if your looking to drift the WRX by making it rear wheel drive, its still heavy and would cost more than an s13 just to convert it properly and even then it would still not be as reliable unless you replace everything from the center diff back and by that time your looking at the same price as a swapped and mildly modded s14 for a stock 3klb rear drive car, not saying it cant be done, but why take away why the car was made?