Yes, a Will can be contested after a Grant of Probate has been issued. In fact, some challenges can only be brought after a Grant of Probate has been issued. This includes Section 117 claims, in which a child of the deceased requests proper financial provision.
Other times, however, it is better to act before Probate is granted. This is particularly true of claims relating to an invalid Will or undue influence. In such instances, it is more practical to raise these queries quickly and lodge a caveat at the Probate Office. Otherwise, a Grant may be issued, allowing the executors to distribute the estate. If this happens, it is possible to make an application to the court, asking for the Grant to be revoked.