If I understand correctly, it sounds like you just need to get correct year lugs for the correct year wheel. In every wheel swap I've ever witnessed the lugs went with their original wheel. See if whoever you traded with has the '05 lugs.
I think you would be making way more work for yourself altering the caps. Try this:
http://www.ebay.com/itm/24-Pc-CHEVY-SILVERADO-1500-FACTORY-OEM-TYPE-GOLD-ZINK-14m-x-1-50-LUG-NUTS-2009-/271938993602?fits=Year:2005|Make:Chevrolet&hash=item3f50d3bdc2:g:vCcAAOSw~CRTpZ4F&vxp=mtr
Thank you owner doesn't have the lugs so I can order these an be fine with installation?