The new version of the importer script is below.
io_import_compile_heart_ism2_20210610
I learned that I can't open another file browser from a file browser to specify an additional ism2 file.
So I decided to specify an additional ism2 file in the cfg file.
Create a text file with the name of the ism2 file followed by ".cfg", and describe the following items in tabs or space delimiters.
1st item ... "bones"
2nd item ... ism2 file name to put on costume (full path or relative path)
For example, in the case of model\attach\dr2001\dr2001.ism2,
create dr2001.ism2.cfg with the following contents.
bones ..\..\chara\c0001\c0001.ism2
If there is this cfg file, bone data is read from the file specified in the cfg file,
and other data is read from the file specified in the file selection,
and a model is created by combining them.