More commonly you have the ability to reduce imports and sometimes to subsidise exports, but once your trading partners have had their say, the mercantilist policy does not reach its goal.
A mercantilist policy works effectively if you have the ability to set your trading partners' policy to (that which you see as) their disadvantage. This is the case when you trade with for your own colonies and can set their policies. It may also happen if the preceding government did not try to act in the best interest of the country, e.g. some kleptocratic tyrants try to optimise for their own good and disregard the country completely.
But for a country where government can neither set its trading partners' policies nor really decide what its companies and people do? Forget it.
Who would benefit most from this?