I just public this bom_plugins/bom2sch.py from here, it may help you to backport value if the custom fields already defined in your schematic;
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python bom2csv.py XXX YYYWhere input file XXX can be root .sch file, or .xml file. YYY is a output csv file name -
python bom2sch.py YYY [XXX]Where output file XXX can be root .sch file. YYY is a input csv file name.