Sure it's really easy, Hit ALT+O to bring up your Options. Go to Controls on the Left Hand Side. Then on the right hand side there are a bunch of options there is one that says Hotbar Keys with a + beside it. If you click it, it will expand to show all of your hotbars. Drag your Transmute spell to one of your hotbars and then right click the hotbar and click Hotbar settings. You will see a Key Map here that tells you what hotbar keymap that hotbar uses. Scroll down in that Hotbar Keys options panel until you find that hotbar keymap and go to the button you put your transmute on. Then click the gray box and press your key.
Here's an example:
http://prntscr.com/mr7lzz
I have placed Transmute on my HotBar #4 on the 6th Button and set it's binding to SHIFT+T and it shows up as St as i have it set to Text style Minimal Text on it.
This should get you all of the way there. But if you have any questions let me know.