Credit question... is this legal?

Okay, so my dad has credit card bills that he makes payments on and the interest is like 20+% and there is almost no way for him to pay it off with that interest rate. He's considering going to a debt counseling place where they pretty much reduce your interests rates to something lower and/or lowers your amount that you owe. However this destroys your credit score. Which he doesn't see as a problem. My question is this: if he was to go and buy himself a new car and then consolidate credit and his credit score was ruined it that legal, because technically he is going to be making the same car payment on time and for the amount that they had negotiated, but his credit will be ruined shortly after. He's not worried about his credit being ruined because he doesn't need or want to borrow any more money anyways. I hope that I worded this so that it makes sense.