If a person signs a Guarantor form (or any contract) yet amends it by marking through disagreeable areas with a black marker or writing amendments on the page THEN signs it... is this a legally binding contract or is it void because of the adjustments?
Depends on whether the "other side" (i.e., the landlord, management) signs it and, typically, initials by each change (to indicate they are aware of these).
If they do, it can be argued that they have accepted the amended copy.