It depends, if the exclusion is on ailment a horse can fully recover from or not. If the horse can recover and there has been no surgical intervention, after the exclusion has been on the policy for at least one full policy term, or if there has been surgical intervention after two full policy terms you can apply to have the exclusion removed. To apply submit a satisfactory Declaration of health form noting there has been no further concerns related to (whatever the ailment was), along with a satisfactory veterinarian certificate with the vet referring to the excluded ailment. Once applied to have the exclusion removed by submitting the forms to HEP – MGA the exclusion may or may not be removed at that time depending of the circumstances and the discretion of the HEP – MGA.
There are some ailments that cannot be removed as the horse would never fully recover.