I'm using the Extended WPF Toolkit's PropertyGrid. For the margin target property I would like to divide it from (0,0,0,0) to four separate fields with words or arrows, similar how it is in Visual Studio. My xaml looks like this:
<extToolkit:PropertyDefinition TargetProperties="Margin"/>
Current visual appearance:

Desired visual appearance:

Not quite what you asked, but something easy you can do is setting the
IsExpandableproperty totrue, like so...That forces the PropertyGrid to expand out the object at that property.
However, if you want to do the editor the way you have it, you have to create a custom editor for that specific property. You do that by associating your own templates for the editor. Since it looks like something that may be reusable, I would design that as a control, then use that control as the editor.