Yep, whip-out the bog and tile under, however, take note (BEFORE you remove the bog) of soil pipe/bog pan spigot height from floor. Why? The floor height will be increased by the thickness of the tiles/adhesive (and any ply you may lay) and so the bog spigot may not line-up with the soil pipe through any wall. This can be overcome by using an offset WC pan connector. If your soil pipe socket is in the floor your existing WC pan connector may be long enough to accommodated the extra height if not then fit a longer one.
Also note position/height of water supply pipe to cistern as this plumbing may need a slight alteration to accommodate the extra height. Tip: it is sometimes easier, rather than trying to add in a short bit of copper to make up the height difference, to cut the supply pipe and exchange for a stainless flexy complete with a service valve.
