I'd like to know if there is a way to write the local filenames to be identical
to what appears in my web browser window except replace question mark, ?, with
pound sign #, or underscore, _.

The site I want to mirror has many, many query variables after the ?, so the
'%[param:before:after:notfound:empty]' advanced variable extraction option is
not practical.

For example, I'd like
listing.php?id=96420&click=1
listing.php?mode=&total_pages=321&page=7
listing.php?main=Instruments
contact_seller.php?to=29929&id=96438&title=Summer%27s+Coming%21&return=%2Flisting.php%3Fmode%3D

to be saved on my machine as
listing.php_id=96420&click=1
listing.php_mode=&total_pages=321&page=7
listing.php_main=Instruments
contact_seller.php_to=29929&id=96438&title=Summer%27s+Coming%21&return=%2Flisting.php%3Fmode%3D

There are too many query parameter variables to use the
%[param:before:after:notfound:empty] option. I do not know all the variables.

Isn't there a way to just replace the ? with another character for saving the
file?
Thanks