(NOTE: This is a secret that was supposed to be posted on GameFAQs but the admins are too stupid to know it fits their guidelines. Anyway...)
Go to Creation Center and then Create/Edit Uniforms. Select the team you're facing. Then either select or create the uniform you want your CPU-controlled opponent to wear. Now click the Left Analog Stick to set it as default. Now enter Connected Franchise Mode and click the Right Analog Stick to create new character. Choose player, coach or owner but make sure to pick the team you're facing. Now go back you your team and play a game. Your CPU opponent will be in the uniform you want.