Steven P. McNicoll wrote:

The rules are not safe where two aircraft can adhere literally to their
separate instructions and occupy the same point at the same time.

A taxi instruction is never a clearance to enter a runway, I don't see
what's so difficult about that.

But I'm ready to admit that you're right and I'm wrong. And I was wrong
when I stated in my first post, where all this began, that it can be a
safety issue when one leaves the tower frequency without the tower's
kowledge, too.

If it makes you feel good, continue to change frequencies at your
discretion without telling anybody and if sometimes you'll happen to fly
abroad, ignore local rules when they don't please you. Just please tell
me beforehand, so I can avoid that airspace.

Stefan