Widget for rollershutters in semantic model

You cannot replace the default, but you can replace the widget. That’s what the “Default List Item Widget” is for. Since you have more than one, I’d recommend creating a custom widget under Developer Tools and then you can choose that custom widget when you configure the Default List Item Widget.

Not by default. There is a one-Item-one-widget by default. However, you can reference and represent as many Items as you want in a single widget. For example the following widget shows the current temperature, has a slider to change the thermostat setpoint, and a button that can change the HVAC mode between heating, cooling, and off.

And a quick search shows someone has already published a standalone widget for this: Custom rollershutter widget with preset configuration. You might be able to take inspiration from that.