Thanks for the welcome, and, ah, the beaming. Ouchies. I do miss the old welcome speeches. But back on topic.
I honestly can't see quite how it would speed up nuclear reactions in the star short of warping space-time in the temporal sense. If they can do that, well that's a drastic temporal increase in a localized area. Thus, why even bother with the LREDs? Just fire the subspace weapon at the GTVA fleet and watch the crew turn to bones and then dust in a few minutes. If that is true, however, tactics aside, you're right, temporal acceleration would do very little to a solid planetoid. However, I figured it probably either disrupts space-time in both senses, by forced "collapse", or compression, of space and accompanying temporal dilation (much as happens near a black hole's event horizon), etc, or introduces specific anomalies, be they gravitational or something like a subspace tunnel to remove or introduce material at the core, any of which would be more than sufficient to tear apart a moon.
I do agree, though, that short of a subspace weapon, and maybe multiples of them, you're rather unlikely to find anything in FS2 capable of doing anything more than rendering a reasonably sized solid planetoid uninhabitable (assuming it's not already) and badly cratering - maybe liquefying for a short while - the crust, barring a very, very patient government willing and able to drill out a huge cavity in the core and pack it with meson bombs, or design a super-large one in-place.