Hi Jackerouac,
1. You can contest the will if you are a child of the deceased or someone who was maintained by the deceased immediately before her death.
2. You can challenge the validity of the will/amendment on the ground of lack of testamentary capacity (i.e your grandmother was coerced into changing the will, she did not know what she was doing because of illness that significantly affected her capacity to leave gifts to people etc). This is generally quite difficult but if successful, the change/new will is invalid.
3. The executor has 1 year grace before distributing and may extend this period with leave fro court. This is because there are time limits for when unknown creditors may claim against the estate and unknown beneficiaries need to be found or new eligible persons may contest the will. The executor should not be distributing property before these time limits have expired.
4. The executor should not be dealing with the estate until they have obtained a grant of probate. Otherwise, any dealings which are later successful challenged can be accounted against the executed personally. Which means, the executor may be liable to pay back any loss or disadvantage incurred by a beneficiary due to the executor's mismanagement of the estate.
5. However, the estate immediately vests in the executor after the deceased's death. This means, the executor has legal right to deal with the property as they like as long as it is in accordance with the will. The executor owes a duty to the beneficiaries as a whole to manage the estate in a proper manner and in accordance with the law relating to wills and probates. This duty stems from the will itself.