AMENDMENT TO TRUST AGREEMENT

Exhibit 10.49

AMENDMENT TO

TRUST AGREEMENT

WHEREAS, Dynegy Inc. (“Dynegy”), Illinova Corporation (“Illinova”), Illinova Generating Company and Ameren Corporation (“Ameren”) entered into that certain Stock Purchase Agreement dated as of February 2, 2004 (the “Agreement”) under which Ameren will acquire all of the outstanding common and preferred stock of Illinois Power Company owned by Illinova;

WHEREAS, in connection with the transactions contemplated under the Agreement, the Illinois Power Company Incentive Savings Plan (the “Plan”) will be amended in certain respects (the “Plan Amendment”), including being renamed as the “Dynegy Midwest Generation, Inc. 401 (k) Savings Plan,” effective immediately prior to the “Closing Date,” as such term is defined