Hey!
O-ring mods won't ever have a problem because all keycaps have the same stem width, so that won't be an issue. However, for putting on custom caps, like minho said, there are some strange sizes. It has a 6.5x spacebar, as well as a weird variety of 1.5x, 1x, and 2x (what it appears as, anyways), so you wouldn't be able to replace all of the bottom row. Something to consider, though, is that the Corsair spacebars have an engraved texture which lasts and is overall quite nice; perhaps you won't want replace it even if you could.