Nothing in this part requires you to modify or abrogate an existing concession agreement (one executed before April 21, 2005) during its term. When an extension or option to renew such an agreement is exercised, or when a material amendment is made, you must assess potential for ACDBE participation and may, if permitted by the agreement, use any means authorized by this part to obtain a modified amount of ACDBE participation in the renewed or amended agreement.