I'll cover this if nobody minds.
to create a new char.lgp tools you use your chosen lgp tools, then choose, 'create' (at least for ficedula's anyway) and then when it asks for what files it shall make the new lgp file from,
choose the folder that you made the changes to (this case, char folder inside the FF7 directory, data, field directory) and then chose to save the new lgp file as char.lgp either as the char.lgp in the field folder inside the data directory, or anywhere else on your PC.
i hope that answered your question.