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:

YouTube

Short 1/4" aid bolt
Old 1/4" bolts and a short 3/8" bolt
A very rusty, short 3/8" climbing anchor bolt. The replacement was a 1/2" x 2.75" stainless 5-piece bolt in the same location.