This not done in general. Some symbols are manually created (think for example of the symbol for a nand gate) and adding another pin in the schematic is difficult to do automatically. The more artwork is done on the symbol the more difficult is to decide where the additional pin needs to go.
Pressing 'a' in the schematic after adding a pin will regenerate the symbol as a 'box' symbol. the order of pins in the symbol reflects the vertical ordering of pins in the schematic.