Overriding parts of acts_as_taggable

Hello,

I would like to override parts of acts_as_taggable plugin. In
particular I would like to override some of the functions in tag.rb and
acts_as_taggable.rb. What is the best way to go about doing this. I put
something like this in RAILS_ROOT/lib/acts_as_taggable_helper.rb, which
is a file I created:

class Tag
  def my_method
     # do some stuff here...
  end
end

But it didn't work. What is the best way to go about doing this without
altering the original files.

TIA.