Yeah if its something like OpenWRT, you could perhaps schedule a job that runs daily that swaps the creds and reconnects. You wouldn't need to get new cabling or
ONT etc. Basically have it provisioned from BSNL, and alternate the credentials used daily.
With the 1277 plan x2, you get 1500 GB at 100 Mbps.
Having said that, if you have Jio as an option, and don't really mind its cons, then Jio might be cheaper and faster at that price point.