Just wondering in the case of gunner and hotshot copilot if when spending focus tokens you had to change your focus results.

No, to my knowledge not.

You can spend a focus even if there are no focus results. But spending a token for its effect will have its effect.

No. If you spend the token to change results you must change all results.

You must always spend a focus to do something; the something is a named effect which might not actually change the game state, but it must be an effect you could legally invoke.

So you can spend a focus to change 'all focus results to hits' when there are no focus results in the dice pool, but you can't spend one for no reason.