On the assumption that Homie does not support any kind of roller function?
And you would therefore define two command topics at your device, a numeric for position command and a text for up/down/stop command?
(plus position reporting via another topic?)
Okay, so stick with your RollerShutter Item, and number channel link, Set up stateTopic and commandTopic for the numerics.
This will ignore UP/DOWN/STOP. (as you’ve already observed)
Now set up another string channel with commandTopic. No stateTopic. Use transform if needed (I think likely not) to convert UP/DOWN to string “UP”/“DOWN”.
I do wonder if you might need the transform to filter out numerics though.
Link this write-only channel to the same RollerShutter Item.
If that’s unworkable, a secondary String type Item may be need for the textual commands. With a rule responding to original Item commands, and reposting to the String dummy.
You’ll almost certainly want autoupdate false on your RollerShutter Item to stop that interfering with status.