"of" that farm could also possibly just mean living there....depending on space for writing.......maybe similar to the term "of this parish"
Conventional wisdom says that 'of' followed by the name of a place within a parish specifically indicates ownership, 'in' implies long-term residence and 'at' implies short-term residence.
Out of curiosity I have just checked my records and of 715 marriages in Scotland transcribed from the parish registers, only 121 contain the phrase 'of this parish' while 342 say 'in this parish'. 56 say 'of the parish of' and 166 'in the parish of'. So although 'spinster of this parish' is a sort of cliché, 'of' is actually less common than 'in' (in Scotland, at any rate).
I also note a couple of instances where, the banns having been called in two parishes, the register of parish A describes the couple as 'of this parish' and 'of the parish of B' while the register of parish B describes the same people as 'in the parish of A' and 'in this parish'.
So I deduce that nothing can be read into the use of 'of' or 'in' when it refers to the parish as a whole.
I cannot think of an easy way to check the usage where the person involved is described as 'of' a particular place which is within a parish, but in a quick check of some baptisms all those where the parents are described as 'of' do refer to people who owned land; I know they did because of the registers of sasines.
To disprove the conventional wisdom stated above would require finding a reference to someone being 'of' a particular place whom I know not to have been the owner of the place in question. So far, I have not found such a reference.