Yes.

This is what the Flux documentation says about the topic:

"Defines a set of widths which will show up in the Context Menu for easy access. The keyboard shortcut W will cycle through the set. Example 1: Suppose you know you will be alternating between routing power traces and data traces. Add the Preferred Trace Width Rule to the Object-specific Rules of the Nets object located in the Objects panel. Then, in the entry box input the desired widths of these two types of traces, (150um and 500um for example). When routing, press w to easily alternate between these trace widths."