if there is already an existing tenancy agreement (with an option to renew clause in it) then there is no need to execute a fresh tenancy agreement to enforce the renewal period unless of course the parties wants to incorporate new terms in it or to extend the tenure for more than allowable in the option.

a simple letter indicating the exercising of the renewal (with ad valorem) stamp would suffice and no, now lawyers are required to be involved.

all documents are required to be stamped no later than 30 days from the date of the instrument, so unless the parties want to back date the letter, the letter can be dated current and then stamp without penalty.