That would probably work (the devil is in the details) but it wasn’t really designed for that purpose. Once you get caught up on measurements, the expectation is that new measurements would not be based on historical data, but rather actual new inputs to IoTaWatt that would have no history. So they would just be added to the measurement set and start up from now.
If you were to discover in hindsight that there is something that the IoTaWatt was measuring and you haven’t been sending to influx, then yes, you would need to upload everything again to achieve that.
But I would not recommend changing to a new id tag. That would have a ripple effect in your queries. I would recommend that you stop the influx service, drop the entries from all series with the present id tag, set the upload history from to the appropriate date, and restart the influx service.
Remember the six-P principle: Proper Planning Prevents Piss-Poor Performance (Woody Allen)