I purchased a Beretta 90-Series pistol. It has a plastic recoil spring guide rod in it. I prefer the old-style steel one. Will Beretta replace it for me at no charge?

90 Series Recoil Spring Guide Rod

The short answer is "no."
The polymer recoil spring guide rod was adopted by Beretta years ago after extensive testing.  The polymer material is as durable as the steel guide rod and in some respects, offers superior characteristics.
Additionally, Beretta has furnished the polymer recoil spring guide rod to US Armed Forces for use in the the M-9 pistol.