ninjigalaxy sent me an explanation of how picross boards are stored in mario's picross' rom and commissioned me to make a tool to inject custom ones
after i made that i wanted to figure out how to replace the text and i've been moderately successful at it
the download contains three scripts:
picross_board_main.py
replaces a board in the ROM with a new board
from a text file or small image
picross_dump_text_main.py
dumps dialogue and puzzle names to editable text files
picross_replace_text_main.py
lets you replace dialogue or puzzle names
with a file dumped by the abovementioned script