I am actively involved in sustainable anchor replacement. There are thousands of rusty bolts that need to be upgraded to stainless, modern, climbing-specific hardware instead of cheap masonry fasteners originally designed to affix signs to brick walls. I have many YouTube videos describing the necessary tools and techniques for removing bolts so that the original hole can be made larger and reused. Drilling a new hole next to the old bolt is less than ideal – remember that every bolt does leave a permanent mark on the cliff. Drill judiciously.
My YouTube channel is where you will find content on bolt replacement along with bulldogs and some guitar stuff: