Maryland Code, Commercial Law § 2A-208

(1) An agreement modifying a lease contract needs no consideration to be binding.

(2) A signed lease agreement that excludes modification or rescission except by a signed writing may not be otherwise modified or rescinded, but, in a consumer lease such a requirement on a form supplied by a lessor must be conspicuous.

(3) Although an attempt at modification or rescission does not satisfy the requirements of subsection (2), it may operate as a waiver.

(4) A party who has made a waiver affecting an executory portion of a lease contract may retract the waiver by reasonable notification received by the other party that strict performance will be required of any term waived, unless the retraction would be unjust in view of a material change of position and reliance on the waiver.