Mounted sizes

depends on the binding. On fks its like half a size at most, on a lot of other bindings it depends on the track length and where on the track it is mounted.

^yep track bindings will be the best for adjustments but 2 sizes bigger or smaller will be pushing it. Although the heel may move that far you don't really want to be riding at the extremes of the track as it will cut down the movement available for forward pressure.

It might work, but that doesn't mean it's safe. If the forward pressure is off (which it will be if the bindings are set for a different size boot), the skis may not release if you crash, even if your DIN is low. Even two pairs of boots of the same size will sometimes be slightly different, enough so to require a forward pressure adjustment. If they are close, the bindings can be adjusted without redrilling, but you have to know what you're doing to get them set exactly right.

Your bindings can be adjusted to accomodate a different size boot, but take them to a ski shop and have a ski tech adjust them (definitely forward pressure, maybe toe height, not sure about the latter; ask about both to be sure). If they need to be re-drilled it can be anywhere from $30-$60 for a pair of skis depending on the shop. If they only need minor adjustments and don't need redrilling, some techs might do it for free, some will charge you, but it will be cheaper than redrilling. Even if you have to pay, it's worth it to not get a broken leg.