Free speaker tweak that's a must do

I have been doing this myself for a few years. Really tightens up the imaging and bass response. You may also look at replacing the screws with soft brass replacements. Driver magnets and steel screws are not a good match for spurious wave interaction. Some manufacturers even recommend it. Enjoy!

Keep in mind you can over torqued them and they will just loosen again. I suggest thread locking compound if loosening on you. And the brass screw deal. The magnetic force is very very small and far to far away to have any effect on transducer. But if you feel this maters have at it just don't snap a fastener brass isn't so strong.

Most speakers should be tightened every 6 months or so depending on how loud they are played.

Only in case if you receive ones with ones that you can unscrew with fingers.
Overtorque may be worse than under.

I would suggest using a non-magnetic screwdriver. Some driver magnets are surprisingly strong, and can seem to reach out and grab a screwdriver, leaving a punctured driver in it's wake.