Just noticed this useful reference from West System when researching another topic, and see it’s the same one mentioned by Waltthesalt, above:
As he said, it discusses the various procedures for core repair. Also, it goes into the advantages of repairing from the interior and exterior (middle of p33). Pretty much what I said earlier about not disturbing molded features like nonskid, if another method is reasonably feasible.
If you read this pdf, core repair and all related tasks should become very clear.