What is the ruling on not implementing an unwritten fatwa that diminishes the heir's right and transfers it to someone who is not in need of it, and is it permissible to take financial compensation for it?

It is permissible in Islamic law for the testator to revoke their will entirely or amend it whenever they wish. Some scholars have reported a consensus on this matter. The testator has absolute freedom to revoke and amend their will, even if it was written and documented. However, if the will is from someone else, it is not permissible to change it as long as it is lawful, even if it affects your share of the inheritance or if the legatee is wealthy, because the will is the right of the testator alone, and "as for those who alter it after they hear it, the sin thereof is only upon those who alter it."