I'm trying to find a move that switches 2 corner cubies of Rubik's Cube without disturbing the other 6
If you don't care what happens to the edges, you could do
$$ RU'RUR^2F^2RFR'F^2 $$
which interchanges the two top front corners and leaves the 6 other corners untouched. (By exhaustive computer search, there are no solutions shorter than this, in either the half-turn or quarter-turn metrics. Interestingly, this shortest solution only upsets 4 edges, even though the search allowed for arbitrary disruption of edges).
If all edges must remain untouched too, then the task is impossible, as Doug M explains.
And then a move which fixes the position of the back corner cubies and one front corner cubie.
A standard 3-cycle commutator will do that, this time leaving the edges alone:
$$ U'FDF' UFD'F' $$