The magnets have nothing to do with the function of the lock ring. The kits that FDV sells are a higher quality improvement over the often weak stock magnets found in some clones... the purpose of which is simply to provide a repelling force for the button.
The PVD (Physical Vapor Deposition) coating (assuming this is a higher quality piece and it's not just paint) - if the lock ring is overtightened - can produce a hard, gritty spalling effect - sufficient to bind the ring.
Sometimes freezing and/or heating in hot water can be sufficient to allow the parts to separate... I'd disassemble the button first so you have better purchase on the ring. Make sure you're turning the ring in the right direction. (Yeah... I know, but it happens
)
On occasion, it may be necessary to use a liquid penetrant to unbind the joint... a product like "
PB blaster" penetrant may help.
