I tried to do this mod with a UT139C and it worked with almost no setup
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
I adjusted the LCD biasing and prevent the backlight to auto turn-off.
I soldered header pins on the board, connected pins to Arduino as shown by @KBird, read the sketch of @frozenfrogz , try to understand what was doing and what was going to happen, uploaded et voilà. Done.
I have a question as I'm quite new on this: the methods that do the bit write are into the loop(). I'm not sure if I did the correct thing, but I waited for two loops (one to see the dump before, and the next to see the dump after and check if bytes were written), and after all bitwrite functions executed i pulled out the 3v3. Did I act correctly or are there less agressive ways to break or stop the loop once everything is done?
Thanks to all people that investigated and made this possible, btw.