Can I refrigerate pre-wrapped fresh lamb in its store wrapping?

Yes. In fact, it is recommended. Food scientist Susan Brewer, Ph.D., explains why:  “In the U.S., most  red meat and poultry in the retail case is packaged in modified atmosphere packaging, which is high in carbon dioxide.  The purpose of the CO2 is to suppress microbial growth.  If you unwrap the meat, you lose this protection.  In addition, every time you handle the meat, it becomes contaminated by air, hands, and contact surfaces.”
 
Source(s):
Brewer, M.S. and Chapman-Novakofski, K. 2006.  Meat Safety for the Consumer, University of Illinois Extension.