Yes, most Pitstone homes can be extended, and the heritage rules mainly affect the older corners. Listed buildings are few, and most of them are Grade II. There's one conservation area nearby. The housing is mostly post-war and lightly protected. The neighbours are applying for planning permission all the time.
Historic England lists 35 buildings in and around the village. Two are Grade I, two Grade II* and 31 Grade II. Listing covers the inside of a building as well as the outside, so in a listed home even a new window or a moved internal wall needs listed building consent on top of any planning permission. In a village where most homes went up after the war, those 35 are a small, well-known group, and buyers of one of them know what they're taking on.
The area has one conservation area, at Ivinghoe. Inside a conservation area the council looks harder at anything visible from the street, and some work that would be routine elsewhere needs consent. Ivinghoe got the conservation area and Pitstone got the cul-de-sacs, and with them a much easier planning life.
There is one scheduled monument in the area, the strictest tier of heritage protection. It matters to the handful of owners whose land comes near it and to nobody else.
The planning records hold 1,085 applications between April 2024 and June 2026, and 584 of them in the last twelve months. People here extend, convert and rebuild all the time, and none of it is unusual. Nobody buys a three-bed semi under the Chilterns and stays content with three bedrooms for long.
For an unlisted post-war house outside the conservation area, much of the ordinary work, such as a modest rear extension, a loft conversion or a porch, can often go ahead under permitted development, with no full planning application. Bigger or more visible projects need planning permission, as they would anywhere. Newer estates sometimes had permitted development rights removed when they were approved, so check Buckinghamshire Council's planning portal for the address's own history and any conditions attached to it.
Your freedom to extend here is middling. It's easy for most of the village, and much harder for the owners of the 35 buildings that history got to first.