Sneak Attack Damage

I believe there are no STR modifiers for damage in LotFP, and sneak attack only modifies damage, so there is no conflict there.

If magic is modifying damage, I would take it on a case by case basis - some magic may make sneak attack less likely or impossible. If it’s just a magic enchantment on a knife providing extra damage, I would say it happens before the sneak attack modifier.