Landlords need to be aware that when they have a Surety Guaranteeing, for example, a tenants obligation in a Lease, that it is possible to undermine that protection by reaching further agreements with the Tenant.
If there is any variation to the terms of the Lease, unless the Guarantor has provided formal written consent to it, it is quite possible that the event will have triggered a release of the Guarantor to his responsibilities under the Lease.
There may be arguments about the nature of a variation being able to trigger a release but clearly it is sensible not to create an opportunity where the arguments can even be raised. To prevent the Guarantor from having that opportunity they need to be joined as a party to every written document which relates to the Lease. This should be done even where as Landlord you are aware that the Guarantor knows of the proposed changes and has agreed to them. Failure to take such action has the potential to let the Guarantor walk away from the obligations previously had under the Lease.