This will likely work as it is the same as deleting the part and re-adding the new one with the new footprint. With 44 pins or more, I was trying to save some time and potential errors of not adding the correct signal to a pin.
Ah, but if you delete the part without first disconnecting the wires, the wires connecting to the part will also disappear. If you disconnect wires, replace part (with one with an identical symbol, or at least with identical pin positions and origin), connect wires, then there is nothing more to do, no wires to replace. If you disconnect, delete, add part -- you have to position the part correctly. If you just replace, the symbol will appear in exactly the same place as the original. That seems a bit safer to me, and a bit easier. But of course you are right, you can accomplish the replacement by deleting the original and placing the new part.