So, you can only apply an effect to a custom spell three times max. Say I start with the Basic Spell Fire Blast (d6) and apply Dice Upgrade thrice (d8 => d10 => d12). If I then apply Powerful to the same spell, one of the options is to upgrade the dice. Is this the “same effect” even though it’s technically a different effect? Is d12 the limit, and if not, where do you go from there? Break out the DCC dice for d14? Or skip right to d20?
(This is only a hypothetical, because in practice the best option would be to use Powerful to add another die of damage instead, giving you 2d12.}