Most of those connectors don't pull out the back. You push the wires through to the front, undo the crimped pin or socket, then you can pull the wires out the back and swap them over.
There are little prongs on the pins that stop them from moving once they are in position. If that is the problem you are having, get some fine nose plyers and pull them, forcing the prongs to bend. They are easy enough to bend back into position.