The two sets in question are the
Invalid Link Removed and the
Magma TRANSPOSITOR MI-E BASS SOUND (GCT-E). Yes to the first question (nut groove enlargement needed) and probably not to the second (bridge tie block hole widening): since these strings have to be tied like normal classical guitar ones, their ends are actually thin enough to go into the holes (I can't vouch for the treble string holes though, but I suspect you'll be fine, and not need to widen the holes on those either: cores ergo ends for the new low-octave strings should be accordingly thinner).
They're not heavier-tension than standard classical guitar sets though: they're about twice the gauges (= 4 times the volume per linear inch) but tuned an octave lower, which (assuming construction being identical, only scaled up, which is not a given but not far from reality) equals...equal tension. In fact, one or two strings may happen to be lighter in tension, lowering the total pull on neck and top/bracing.