after reading this some questions come to mind  1st and most importantly do you have the landlords permission to interfere with the router or make the changes that you are doing?  (you already mention the landlord is not bothered, so my initial guess is you might not have permission...??)

the reason i mention this is if this is a boarding house it is now covered by the RTA and if its not a boarding house then thee person who should be calling the shots is the person who signed the tenancy agrmt.  

why is this important well if I was the annoying flatmate and i discovered you interfering with something like internet access I could reasonably argue you are interfering with the use of my tenancy and as such I could go to the tenancy tribunal and the landlord could be fined up to $1000 which the landlord could action against you.

if you don't have the landlords permission to modify or do what your doing it doesn't matter whether you are using MAC filtering or not; this is not something that has a technical solution at the end of the day it is an issue for the landlord to sort our; (either the landlord buys more capacity or puts in something like zenbu, but it is for the landlord to do, not you)

with the capacity been used up then i suggest you put a letter to the landlord outlying your concerns, and indicate that the other tenant/boarder whatever is interfering with your enjoyment of your tenancy.

and the end of the day this is for the landlord to sort the signee on the tenancy is its a single tenancy and or a flat discussion not up to you to put in a solution on your own bat, your asking for trouble.