Respectfully, the crit success/crit fail system, with the magic 55 and 69, is a bit jank. On 1d100, you have an either 2% or 3% crit success rate and 1/100 crit fail rate; on 2d50, you have 3.12% crit success rate and 1/2500 crit fail rate; on 5d20, you have 4.37% crit success rate and 1/3,200,000 crit fail rate.
Seems to me that if you want to replicate the feeling of rolling a Nat 1 or a Nat 20 on a d20, instead of the 55/69 stuff, you could just roll a separate d20 (call it $critroll) at the end of the diceroll and set $skillroll to 1 on a 1 or to 100 on a 20. Would be simpler, and be perfectly consistent between dice settings; would also be a good excuse to replace all the instances of `set $skillroll to random(1, 100)` with calls to DiceRolls, though I admit that's a big refactor.