01-05 are the same base bumper. The valences change from round fogs to square. Then 06-08 was a different bumper with square lights. Then 09+ is that bumper with round fogs.
01-05 4x4/EDGE Bumper with color matched bumper and valence
01-03 Round Fogs (your current)
04-05 Square Fogs
06+ 4x4/Sport Bumper. Only come in Black, DSG, or color matched, chrome phased out.
09-11 Round Fogs
06-08 Square Fogs
If you want to change from round to square you just need a new valence (04-05) with the 04-05 square fogs.