Those of us who have survived ERP implementations know that 'customization' is a dirty word. It's not that it can't be done (it can, as your programming consultants will gleefully inform you), but that it has impacts down the line that you may regret.
According to Jay Deakins, once you take that step you're setting yourself up for scope creep, limited growth, and upgrade problems. Read his article on the Manufacturing Business Technology site to understand his issues with customization
HERE.