Modify the value of an attribute

Modify the initial default value of the property.For example, the initial value of the input box%25~%401KF0WTAZ_DB0VFO49R_B

If I understand you correctly you want to create elements with default initial properties?

For example: the initial value is first_1, not Process_1

ok?I want to set the initial value of the property panel (general id) when the page loads

The default initial id of a newly created process ist harcoded as Process_1 in the Modeler.js and can’t be set in the modeler right now. For all other elements it is filled in the following form: elementType + random suffix. Not sure whether you mean to have the option to adjust this initial id-value for all kind of elements or just when creating new diagrams.

As I understand you correctly you mean the second thing in this case. I’m not sure whether it should be intended behavior do modify the initial id-value for processes. Maybe you can open an issue with a clearly description of the feature you want to be implemented in bpmn-js and we will discuss about it.