Currently, the Image component uses the sprite's pixels per unit variable in order to determine the sizes when slicing and tiling an image.
It is currently impossible for a user to have different slicing using only one texture. The only solution I have found was to duplicate the texture file and reimport it, which quickly bloats the texture atlas.
By copying the Image script, and simply applying a factor to the pixelsPerUnits variable, I have been able to make the slicing manually editable.
It would be handy to either make the pixelPerUnit variable virtual in order to be overriden,