Is there an option to turn off the '.. rst3: filename: file_name.txt'
text added to the first line of your rst3 created file?
@bool generate_rst_header_comment = False
FYI, I found this by searching for "rst3:" in leoRst.py. Searching Leo's sources is the recommended way of discovering arcana about Leo :-) Nobody can remember all the options that exist...
To be clear, this option is present in the rst3 command, part of Leo's core. I have not investigated the obsolete rst3 plugin.