It would be easy and nice feature if we can use the symbols like `NSE:INFY` in stead of instrumentId while websocket subscription. It would avoid downloading the instrument_id.csv and then doing a lookup for a symbol.
Yes, it is recommended to update the file every day. In case of the F&O segment, tokens are re-assigned after the expiry to some other instrument sometimes. In case of the equity segment, when an instrument is moved from EQ segment to T2T segment, the instrument token changes.