Do 3rd political parties realize the power they have to change the outcome of an election?

Greens take votes from democrats. Libertarians take votes from Republicans. Constitution Party candidates take votes from Republicans. However, there is seldom third party candidates on the ballot especially in local elections. e.g. a Libertarian could register as a republican in a republican dominated district; get a friend to register as a Green (thereby taking votes from the democrat), thereby increasing his chances of winning. I have seen this method work in local elections a few times, but not very often.