Brass is non-ferrous and may/should not effect the magnetic field of drivers that use magnets.
Same goes for using non-ferrous mounting gear for many phono cartridges.
Suspect that doing so may make an audible difference on some tweeters/midrange drivers, but never tried it (so don't know).
If a tweeter/midrange is placed close to a woofer, then it would make sense to replace the woofer mounting hardware as well (if experimenting).
DeKay