Because it will possibly restrict pellets when you finally get the thing functioning properly and you'll disrupt the airflow and flame pattern to the point that the electronic controls won't work properly.
I have a Harman. It's a great stove but the there is a learning curve. Don't try to redesign what doesn't need it. Let's solve your problem instead.
Good advice. No white recessed screw and nothing in the manual on Low Draft Adjustment. I'll need to borrow a camera to get pictures.