I am at the early stages of considering renovation of a rubble stone semi detached two-up two-down. The corners of the building are in a poor state of repair. I note that next door has quoins whereas the one I’m looking at does not. Googling has so far failed to answer my question conclusively: can quoins be added retrospectively, and is this a massive job or relatively straightforward? If not, what would the remedial action be? Can anyone help? Thanks in advance!