I'm still waiting for parts to come in, but I think I've found a good way to preserve the 9V barrel connector in case I ever need to use that, and switch between that and the LIPO stuff. I'm planning to follow Morgan Flint's lead and desolder the power switch, cut the existing traces to separate the two halves of the switch, so it will be restored to a DPDT, then connect everything as shown in the pic below. The current OFF switch position will continue to turn OFF the 9V supply, but will connect the charging module to the boost converter input, and the boost converter output to the main board power input. Then what is now the ON switch position will turn the 9V supply ON, but disconnect both ends of the boost converter. I'll have to connect three new wires to the switch pins, but no other trace cuttings are needed.
So if there's no power at the barrel connector, turning the switch ON will turn everthing OFF.
![Smile :-)](./images/smilies/icon_e_smile.gif)
But you can still charge the battery - it's just the converter that gets isolated.
Then I have to see if everything will still fit with the barrel connector left in place. But I suspect there will be plenty of room.
Please let me know if you see any problem with this.