There are a few ways to workaround the nolonger valid <st...> command.

When I started this game, I actually started with a combination of target filters and keyboard key allocation - so all I had to do was switch filters and press the relevant key to rotate to next pc and then cast away lol.

Now I have customised my UI so the party list if to my right of the screen with the enemy list near it, so using my mouse I just click on which party member I want to heal (example) and then TAB or click on the mob to retarget - tbh I have changed a lot of my keys so that they suite my play style which works for me, so the only thing I can suggest is play around with a few setups until you are happy.
If you do, you may find it a good idea to back up your save file first. If you want to know how to do that just ask

Anyway, good luck with finding the best setup for you.