The fundamental terms, supplementary terms and additional terms of a periodic standard contract may be varied (subject to section 127) by agreement between the landlord and the contract-holder.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
This section is a fundamental provision which is incorporated as a term of all periodic standard contracts....