Drag link template

how to change the shape of link while dragging to same as of the template given to link and change the purple border while dragging

like in the picture i want the purple border around “Start” and “End” to change to my will and the link to be like the template of default link defined

You can customize the LinkingTool to get closer to what you want. This is covered in https://gojs.net/latest/intro/tools.html#LinkingToolAndRelinkingTool