Adjust your diet so that you wont gain weight or lose it. Simple as that. Your workout routine doesn't have to change at all. If you eat heps of food, you'll gain, if you eat less foods, you will lose. You just have to find the balance and test it.
I want to maintain those muscles while I keep growing the others that need more inches.
Add extra effort to those muscles you want to work on. Do one extra exercise in the beginning or as a finisher, or even two. If you still keep other muscles active and work them atleast once a week, they'll most likely maintain, and can increase strenght too. No time for extra effort? Superset or take one or two sets from other exercises.
But like Stu said, it's To try something different too, if you have already met your recent goals. Pick new goals. They don't have to be around gaining or losing weight. Aim for results or something completely different.