Radiator replacement & flush

I'm replacing the radiator in a 2001 Honda CR-V because of a small crack in its upper plastic tank (that wouldn't seal after trying a couple of different sealants that promised to work on plastic tanks). I have replaced many radiators before, but I made the mistake of looking at the paperwork that came with the new radiator (Spectra Premium, Part # CU2051), which says I have to use a system flush AFTER I install it or my warranty will be voided. My thoughts are that using a chemical flush is going to loosen all kinds of "stuff", which will probably end up clogging up my new radiator. I would think that, if I'm going to flush it at all, it would make more sense to flush it with the old radiator on it, then change it out with the new one. Ever being the devil's advocate, I started thinking that maybe the flush of the new radiator is to remove chemicals or by products left in it from the manufacturing process (I don't think I've ever purchased a radiator with plastic tanks before). So, I wanted a professional opinion (without regard to the warranty). Should I flush the system with the old radiator on, the new radiator, or not at all?