Can a player spend a fate point to reroll the result of the random spell? I guess not, because of the fate point use list in the official manual. But we have this discussion with a friend.

in our game we use fate agaist random, toadify and other spells with dice rolling. of course if you reroll you must accept the result. I'm not so sure you cannot use fate in these cases.

Using Fate for Random is fine. Remember it's only the player affected by it, and therefore rolling, who can use Fate.

You can use Fate if you have to roll a die affecting your Character. With Random Spell you roll 1 die to determine the effects of the Spell and can re-roll a negative result (same you do with Grim Reaper from Reaper Expansion).

But in some cases, like Toadify Spell from Frostmarch Expansion, the caster has to roll the die for the effect and he can use Fate at will, but target Character cannot. He does not have to roll a die at all, he must accept the result scored by the other player (who can use Fate).