Yes, and with less paperwork than most of coastal Cornwall demands. There are no conservation areas in the village at all. The listed buildings number twelve, and unless you have bought one of them, none of that touches you. Applications go in here at a steady clip. The usual obstacle to an extension in Mullion is finding a builder, not winning an argument with a heritage officer.
On the listings themselves, Historic England's register records twelve listed buildings across the area: one at Grade I, one at Grade II*, and ten at Grade II. Owning one changes the exercise completely. Listed building consent applies to internal alterations as well as external ones, covers things most people assume are their own business such as windows, fireplaces, staircases and rendering, and runs alongside planning permission rather than instead of it. Work carried out without it is a criminal matter rather than a retrospective form. For the other several hundred homes in the village, none of this applies.
There is also one scheduled monument within the area. Scheduled monument consent is the strictest protection tier in the system, administered nationally rather than locally, and it matters to anyone whose land sits on or beside one. For almost every house in Mullion, it is a fact about the landscape rather than a constraint on the kitchen.
The best evidence that people do alter homes here is the volume of applications. Cornwall Council's planning register recorded 492 applications across the area between April 2024 and June 2026, including 213 in the most recent twelve months. That is a village where extensions, garages, garden rooms, replacement windows and the occasional annexe are ordinary business rather than a quiet local scandal.
Practically, the sequence is the same as anywhere. Many single-storey rear extensions, loft conversions and outbuildings fall under permitted development and need no application, though permitted development rights are not universal and can be removed on particular sites or by the terms of an earlier consent, so the first job is confirming yours are intact rather than assuming. Anything larger, anything at the front, anything changing the use of a building, and anything to a listed property needs consent before work starts. Cornwall Council is the authority to ask, and a pre-application enquiry costs less than an enforcement notice. Building regulations approval is separate from planning and applies whether or not you needed permission.
Freedom to alter your own home is one of the real strengths of buying here. Twelve listed buildings and no conservation area means the overwhelming majority of Mullion homeowners answer to the same rules as anyone else in England, with none of the extra layer that makes the prettier Cornish villages so exhausting to own a house in.