I design business process models, not executable programs. I’d like to be able to change the outline of the task box in order to better visually differentiate task purposes and/or categories. For example, when assessing a business model for waste, I’d like to be able to assign different task box outline colors to identify: “Value Added”, “Non-Value-Added”, and “Non-Value-Added but Necessary” tasks.
If I’m not mistaken, you are referring to the BPMN elements. If you’re using Camunda Modeler for Desktop, you may take a look at this plugin.
You can add the code to /resources/plugins and restart the Modeler.