Enterprise standards set the minimum controls every site has to meet, but sites have different equipment, layouts and hazards, so they often need extra controls or different ways of meeting the same requirement. Forcing every site to use exactly the same procedure usually leads to either unrealistic procedures or quiet workarounds.
The cleaner model is to keep the enterprise standard as the base layer and let each site add its own controls on top, with anything that changes or replaces an enterprise control going through review. That way the company can see where sites differ and why, and a change to the enterprise standard still reaches every site.