Yes, you can create expression variables in the Qlik Sense script, and call them when needed.
SET vMeasure1 = date(firstworkdate (Max(Fecha), 1),'DD/MM/YY');
You can call this example variable by entering $(vMeasure1) as a new measure to any user interface object. May I also make a suggestion that you can also fulfil this requirement by creating a Qlik Sense measure master item. With this method, users can drag-and-drop the custom measure to any number of objects on the UI. This method also avoids the need to memorize every measure variable during the development process.