That does work. A lone RoC key will give both RoC and TFT (in Classic mode only, obviously).
I’ve had two verifications so far. First, a friend (who told me verbally). And second, from a post from the other day (they indicate it worked at the end of the thread).
Edit: On second read, they never indicate if they used only RoC or both. So it falls back on my friend’s word. But either way, you already have the TFT key in so you’ll be guaranteed good to go if you put a RoC key in.