Is there a way to use custom POS tagging in LT?

I am building a Java API for the LT. But I would like to use other POS taggers available. Is there a way I can use my own POS tagger and test the LT with that?

Yes, you need to create your own language class, e.g. by extending class English as MyEnglish and then overwrite getTagger() to return your own POS tagger.