Have you successfully executed your code example?
I tried something similar, but could not get it to work. I was afraid newly created characters would replace custom characters previously written. The actual result was even worse.
For me, createChar() had no effect unless followed by begin(). That is the way its usage is described in the documentation. begin() clears the screen, so any previously written characters disappear.
It would be nice to get your scheme operational somehow. It would make character LCDs much more versatile.