No amendment or waiver of any provision of this Guaranty, and no consent to any departure by the Guarantor herefrom, shall in any event be effective unless the same shall be in writing and signed by the Guarantor and the Required Lenders, and then such waiver or consent shall be effective only in the specific instance and for the specific purpose for which given, provided , however , that no amendment, waiver or consent shall, unless in writing and signed by all the Lenders, (a) limit or release the liability of the Guarantor hereunder, (b) postpone any date fixed for payment hereunder, or (c) change the number of Lenders required to take any action hereunder.