Could I substitute brown rice for the white, and simply adjust the cooking time? Or would there need to be adjustments to the amount of liquid, too?

you will very likely be playing w/ your liquid amount anyway, as recipe can cook up differently with @ batch, so adding liquid is no deal-breaker. You might also consider adding in some cooked wheatberries towards the end- for some fun chewiness. (I'm putting wheatberries in alot of things these days!)

i also use brown rice almost exclusively. much tastier and better texture. but i do add a bit more liquid as well as and cooking time.

I always substitute brown rice for white. The cooking time for the rice is the main difference. You will need to either cook it separately and mix it later, or -- what I do -- add the rice earlier. The amount of liquid required is basically the same.