Making alterations to you farm without the Landlords permission was a chargeable crime called Waste, it features quite a lot during the Land War when farm buildings were used to house evicted tenants.
It can sometimes be noticeable how many changes there are to out offices between the 1901 and 1911 census, once the farmer owned the farm (usually just before or shortly after 1901) and no longer had to bow to the Landlord's wishes.