Shutter control: "DOWN_BUT_TILT"

Don’t forget you can uncouple Item state from command by disabling autoupdate on individual Items. (That’s pretty meaningless for Groups though, where the state can only be derived from member Item states anyway.)
I don’t suppose states of string “75%” or whatever are very helpful?

Your underlying problem appears be trying to model a type of equipment that can’t be modelled in a single openHAB Item. You can’t hold both position and tilt status in one Item. You can’t command up/down and tilt in one Item.
So you’re probably compelled to use a couple of Items on the ‘device’ side, and associate them together.
And maybe a third “dummy” Item simulating a combined Item. That one you can send weird commands to, that do nothing of themselves, but a rule can decode to a command sequence for real devices. The dummy can also get its state updated to reflect one or other real devices, or if you wish some combination -“75% down, tilted”

Note, no Group so far. You don’t have to use Groups to create an association of a handful of Items.