Well, if one wishes to do so, then, perhaps, it would advisable to check with your agent.
If the tenancy agreement is already stamped, then, to challenge the admissibility of the stamped
agreement, one should be prepared to answer what makes the prospective tenant to sign in the first place.
If the choice is that the tenant is eager to take a 12 mths tenancy, then, unlikely there is any ground to renege on the agreement.
On the other hand, if the choice is not open to the tenant,( which seems highly unlikely to deny knowledge and anticipation), then, such a situation may be deemed to be known as anticipatory breach of contract.
If so, then, the landlord may seek to enforce his rights under the contract and claim damages for the tenant's anticipatory breach of contract. No right of rescission is open to the tenant since it is reasonably foreseeable that the tenant would have foreknowledge of such a consequence in the event the tenant decides later to terminate the tenancy agreement.