At least tell us which pin is what.
The Arduino Mega 2560 has no I2C bus at pin 22 + 23. Do you want to use a software I2C bus ?
When the SDA is kept high, the SCL pin may be used for other things.
However, if SDA is involved in any way and then you change from Serial to I2C, then the I2C bus might get stuck. That can be unstuck, but might not always work 100%.
Suppose the customer changes a module while the Arduino is running, then there is probably no way to make that 100% reliable.
The RS-485 (a version of Serial communication) is hot swappable.
I'm not sure, but perhaps the SBus (a version of I2C communication) migh be hot swappable.
Combining those with the same wires is not possible.
As you can see, there are many possibilities, but also many things that can go wrong.