You can't do that, that pin name is already taken. You need a new, unique, chosen-by-you name for the HAL pin that belongs to the GUI button.
Bear in mind that this tag only sets the text that appears on the button, not the name of the hal pin....
... So this won't work.
net home-x halui.joint.0.home pyvcp.home-x
Ah, yes. Good point.
You can actually have a pyvcp hal pin name the same as other pins as it evaluates out to pyvcp.halui.joint.0.home so it becomes unique and a valid pin even if it doesn't make sense to do so.
While we are at it, you can add things randomly to the INI file, and you will be able to access them in hal with [STANZA]ATTRIBUTE, but the rest of EMC2 will pay no attention.