[Sombre]

What a first post! I like your attitude.

Like Burn, I will try this when I have time. To answer a couple of questions:

No there isn't a clean way to make mod weapons work with flaming arrows.

Onebattlespell can effectively only point to vanilla spells, so if you had it pointing to a modded spell, that wouldn't work (there is a workaround which is commonly used, I won't go into it unless anyone wants me to). It does work fine with spells that have a fatiguecost of 100+ though, so not to do with gems.