If a cored hull is properly constructed and the core is removed in the areas of through hulls and replaced with thickened epoxy there should not be a problem. The big issue with cored decks is the dozens of ways water can get in, especially after years needing the hardware rebedded and it not being done.
The hull will be solid glass in the keel area and the shaft log and rudder areas. The total number of ways for water to enter, except after a collision, are about 7 through hulls. It they are pulled, core removed around them, and replaced with thickened epoxy there should be no issues.
Living aboard in Victoria Harbour