You are really asking the wrong question.
My counter question is:
Why are you designing your own GND symbol when KiCad already has them in their default libraries?
This has changed in KiCad V8.
I also verified this in one of my own projects. In the screenshot below, I changed the GND text of one symbol to GND1234 and used highlighting to verify it is now no longer connected to the other GND symbols.
