The Rent Ordinance para (e) explicitly precludes that possibility:
Any waiver by a tenant of rights under this Chapter 37 shall be void
as contrary to public policy.
If he attempts to enforce such a clause or in any way dislodge you from the unit, he is liable for a substantial penalty.
I have recently signed a tenancy agreement (England) and have now
decided I do not wish to live there. My guarantor has not yet signed
their guarantor agreement. Does this make my tenancy agreement void?
No. At most, it makes it voidable by the landlord if the landlord doesn't want to enter into a lease unless you have a guarantee (assuming you have ...
A contract can specify the allowed method(s) of payment
If your contract doesn’t then payment by cash is acceptable or any other method the vendor accepts. Your landlord can choose to accept checks and then, they can choose to no longer accept them. Your choice is to either pay in cash or by a method they do accept.