"Learning how to replace a bolt correctly and with the least impact—or supporting others’ efforts to replace bolts—is also critical to sustaining crags and to maintaining access. Accidents caused by bolt failures could endanger access, just as replacing bolts without regard for the best practices in a particular area can endanger it" Access Fund  (US)

For information on fixed anchors and bolting  

https://safeclimbing.org/best-practices-for-hardware-and-placement