Dymamic Icons for Ranged values

[rossko57]

You can use this technique.
Have a scaled Item version of your number, in the case of 0-300 you might divide-by-ten for sanity. You can do that with rule or perhaps transform depending on data source.
Then arrange an icon set as you wish for 0-30 values.
Display that Item in your sitemap or HABpanel, use a multiply-by-ten transformation in your state presentation format to restore the original value for viewing.

[SOLVED] Custom dynamic icons

That is correct. What you might do is update your Number Item using an MQTT transform, so that what is passed to the Item state is degrees-divide-by-10 e.g. 0.0 to 36.0 Then that will work with your renamed icon-0 to icon-36 In the [ format ] part of your Item label you can use anther transform to multiply by ten, to get your original heading back for display.