Shower diverter Height?

Is there specific height/code for installing a shower diverter?

I don't think there is a code issue...installing it at conventional heights may make it easier to sell in the long term, but if you don't care, put it where you want it. Stand in the shower, reach out, and see where your hand falls. Typically, the valve is around 48"...you could make that lower or higher and put the divertor where you want. "conventional" locations haven't necessarily kept up with typical people sizes, like the height of a kitchen counter is based on the right height for a 1950's woman, and people are on average a lot taller now, but the height hasn't changed.