Replacing a schematic component by a connector
You should not do that.

The part that will be placed on the board is a connector.

If you gave the connector a potentiometer symbol, the layout designer would be surprised to find a connector footprint at that location. The people who build the board would be very confused when the part that arrived to be placed in that location turned out to be a connector. People debugging the board would be confused to find a connector there instead of a potentiometer, etc.

If you want the schematic to be clear, you should add the value of the pot to the text where you currently have "Off board potentiometer". If you really want a visible clue about the connections of the potentiometer, you could add a symbol, purely using drawing elements showing which pins connect to the ends and the wiper.