My systems has mostly 5V grove sensors. I am building grove boards that have 3.3V sensors. For cleaner wiring, I want to leave 5V on the grove bus channel and use external pull-ups to 3.3V on the external board. This should work if I remove the SDA and SCL pull-ups from a multiplexer channel so it depends on the external pull-ups instead. Then, the channel has 5V power but 3.3V data pull-ups. There is a 3.3V regulator on the external board.
The question is, which pull-up resistors on the multiplexer board are used for which channels? It is the V2 board.
The whole bus segment will be 3.3V data. Currently there is no 3.3V supply in the system but if there was an external 3.3V supply in the system, it could be wired to multiplexer board and jumper cut as in specification.
1- add a 3.3v supply to system, add two cables, one to power the 3.3 supply and one to feed the 3.3V multiplexer channel and cut jumper, us existing grove jumper on new 3.3 channel.
2- remove multiplexer pull-ups, use existing 5V grove jumper to sensor board which has 3.3V regulator and pull-ups.
So it come down to less wires and hook up instructions. Since you have the schematic, it would be easy to say something like: CH1 pull-ups are R4 and R5 by J2 (JUST A GUESS NOT VERIFIED)