It would be easier to just copy the tiles you want into a new A5 sheet so you can set the 4-way manually. You might need to draw a map with them and take a screenshot to get the different versions.
Also, the whole X/O business is a red herring that is only used in the editor and not even saved as part of the tileset. For non-autotiles, X means it is impassible in all 4 dirs and O means that it is passable in at least one dir. Changing X to O makes the tile passable in all dirs, changing O to X makes it impassible in all dirs, and changing X to * makes it passable in all dirs.
For autotiles, O means all 48 versions are passable in all 4 dirs and the tile is impassible to boats and ships. For A1, A2, A3, and even rows of A4 an X means all 48 versions are impassible in all 4 dirs. For certain A1 tiles an X means it is passable to boats and/or ships. For odd rows of A4 an X means the outside borders on top, left, and right edges are impassible and the rest are passable (see the non-autotile cliffs in A5).
For more info:
Help -> Contents -> RPG Maker VX Ace -> Reference Material -> Resource Standards -> Tilesets.