Here, adding “can” makes it sound just a little bit less powerful. The “can” means that you are not yet guaranteeing anything — you are able to if you decide to do so. However, if you were replying to someone who suggested that you couldn’t, using can with emphasis (stress in speech, underlining in print) would be a natural way of negating the negation. BTW, I don’t know the whole context, but perhaps “is good” should be “will be good”? Also, you may want a more specific adjective than “good”.