Mine Is expected to come here on Monday, Longer Travel, also German Customs Processing can take a bit.
The Fan Screw thing is, in case it protruded from the Surface, because you for some Reason Messed with Those Screws like:
https://forum.krontech.ca/index.php?topic=611.0 The Removing of that Screw a bunch of time really did damage it a bit and some of it now Protrudes a bit from the Screw Head, but still not beyond the Mounting Face of the Camera. Tried to take a quick Picture with an Projection lens, didnt really want to get a real Macro Lens out right now, hope still Sharp enough to see things well enough.
In bad cases i assume this could mean the Adapter would not sit flush with the Front Surface of the Camera, leading to the Adapter possibly getting Scratched, bent if a lot of force is still used to tighten, or just sitting slanted on there, which will mess with your Focal Plane (
https://en.wikipedia.org/wiki/Scheimpflug_principle ).
As they probably cant guarantee, that all screws are always Perfectly to Specification (normal Fan Screws are not exactly high Precision Parts by any Stretch), or that nobody put a Screwdriver on one ever and Deformed the Head a bit, they just have you remove it just in case i assume. Warranty and Stuff, because as a company you will be held responsible if your Product damages something else and such, so why even risk that, if it can be avoided (even if that might be a rare case).
I dont see, why you would not be able to just leave the Screw in there, if you can make sure, it for absolutely sure does not Protrude beyond the Mounting Surface at any Point on your own.
I personally never Removed a Fan Screw for Mounting any kind of Adapters Like this, but i must say, i also Checked if My Screws Protrude before Mounting.
So if yours also dont, you should in Theory be able to just leave it there, if you like. Or, if it protrudes, take it out, grind the Head down a tiny Little bit on some Sandpaper or a Small Belt Sander or something. Or might as well just remove it...