Not possible to do with any PTCL provided Modem/Router combo as far as I know. You'll have to get a router that supports DD-WRT or some other variant like OpenWRT to achieve bandwidth limitation.
Just buy another router with Bandwidth control option and run 2 wireless network. I have done the same in my home. Some basic routers from TP Link offer bandwidth control functionality. DO NOT try to flash any custom firmware on PTCL`s router
Although it does have option for QOS settings per IP basis but it is very hectic procedure (requires to enter each and every IP address) plus some of the parameters are not well known to me.
Although it does have option for QOS settings per IP basis but it is very hectic procedure (requires to enter each and every IP address) plus some of the parameters are not well known to me.