Does this do what you are looking for?
I think you are asking to mount the 555 on the bottom of the board which requires the pads to be inverted. If the pads want to be on only one side use a single sided board. The difference between the two chips in the png is that the one on the right has pcb layer top set in inspector and the one on the left (which is what I think you want) has pcb layer bottom set in inspector which inverts the footprint. So just select the 555 in pcb view and change from top to bottom should do what I think you want.
Peter