It is hard to tell without seeing the definition of your BedroomBlinds-item, but I assume this item is connected to a binding that communicates directly to whatever type of “blinds controller” you have installed.
If this is the case, I think you best (and only?) option is to introduce a proxy-item (take a look here for an example)
The reason that what you have shown above is not working, is that at the time your current rule triggers on the command, the same command is most likely already being processed by the binding, meaning it is really too late to stop it - unless, of course, you have some kind of “cancel” or “stop” command that you can send.