I think this is a hardware limitation.
Standard 2x16 lcd display usally use HD44780 chip, which CGRAM can only store 8 (5x8 format) or 4 (5x10 foramt) user defined character.
To display a text composed with all the 29 specific character, you will have to send each specific character on the CGRAM. Then display it (the specific charater is stored in the DDRAM), and do so 8 by 8 (or 4 by 4) for the whole text.
I think this is a hardware limitation.
Standard 2x16 lcd display usally use HD44780 chip, which CGRAM can only store 8 (5x8 format) or 4 (5x10 foramt) user defined character.
To display a text composed with all the 29 specific character, you will have to send each specific character on the CGRAM. Then display it (the specific charater is stored in the DDRAM), and do so 8 by 8 (or 4 by 4) for the whole text.