Trouble is a relative term: there's legal trouble and then there's "reputational" trouble. Can't help you with the former, you'll need a lawyer for that because I have no clue. "Reputationally" I'd say you're okay "adapting" someone else's techniques/styles but that you should probably give credit if at all possible. "Here I'm using the Ascension Method of xxx" or something similar. Wholly copying something is not really cool but if you're building substantially upon something already existing and extending it I doubt anyone would fault you for not reinventing the wheel. I think you see this a lot in traditional art circles. Of course, I'm not an expert in this area either...so I'd be interested in hearing what others think.