When you create or modify a filled region (hatch) - you can control the pen. I have an image attached for reference.
you know - that is a really good question - I did some looking and I am not finding anything specific to control it..
What I did find - under VV or VG you can control the pattern but not the pen weight. Image attached
but on others you can control the pen weight. image attached.
I looked under the object styles and was not able to find anythng there that corresponds to the patterns or lines.
So very interesting question - maybe someone else has some ideas!