Could work but MAC addresses can be changed sometimes in the computer - so it is fixable, though it may not be obvious.
Enabling security would just have them reset it as they couldn’t connect anymore, so no that’s not going to work for long unless they just don’t use the wireless option.
You could also reduce the signal strength on some routers, might be strong enough for them and they may not notice, or perhaps think it’s just getting old and the range is decreasing, but you may be able to decrease it so you can no longer access it.
If you can login to the router, this would be the best option.
Yes, the person on the computer might figure out why they are blocked, or login to the router and un-blacklist their computer. Or change their MAC. But if the person you are trying to challenge is this sophisticated, you’re fighting a losing battle and getting the neighbour to change their wifi to secured is the only course.
Once you blacklist the MAC address, put a new password on the router admin (not the wifi) to prevent the MAC blockage being changed. A clueless neighbor will probably never touch their router admin as long as their wifi keeps working, so won’t realize you changed their admin password.
As I said in my earlier post - *“surely it would be better to take more control of the computer’s use, and possibly to instill some sense of right and wrong into the person concerned. Stealing bandwidth is - well - stealing.”
*