Retraining Archetype

Question

I'm playing a Lv5 Bladebound Magus, and I was thinking of retraining using the Ultimate Campaign Rules and adding the Kensai Archetype. I've figured out the rest of the class except for the diminished casting. My DM and I are arguing back and forth about it. Do I need to retrain one spell/day out of every Spell Level or retrain reduced spellcasting across the entire spells class feature in a single -1 sweep?

I.e., the difference between one session, and three sessions (one each for cantrips, 1st, and 2nd level spells).

Answer 1

Retraining:

To gain an archetype that replaces standard class abilities you already have, you must spend 5 days for every alternate class feature you would add, subtract, or replace by taking that archetype.

Kensai:

Diminished Spellcasting

A kensai may cast one fewer spell of each level than normal. If this reduces the number to 0, he may cast spells of that level only if his Intelligence allows bonus spells of that level.

Diminished Spellcasting is one new feature; it takes 5 days to retrain.

However, this GM would allow those 5 days to cover all of the other ... fiddly changes to features: Weapon and Armor Proficiency, Canny Defense, and Weapon Focus.

Beyond 4th level, Perfect Strike would take another 5 days.

Note that this GM tends towards leniency with retraining, especially if the player is new, the character isn't working out as well as hoped, or the target of the retraining is new to the player; in all cases, the new option fitting in with the old character's general concept helps push me further towards leniency.

Answer 2

Double checking the rules, magi can only retrain their Arcana and bonus feats as part of retraining class features, meaning that they cannot retrain spellcasting or spell slots.

For retraining archetypes the rule works as the following:

To gain an archetype that replaces standard class abilities you already have, you must spend 5 days for every alternate class feature you would add, subtract, or replace by taking that archetype.

Which means you will spend 5 days per ability that the new archetype replaces. It will take you some time.

A raw reading suggests that retraining into Kensai would take 60 days, as the archetype adds/subtracts/changes 12 class features. But it would make a lot more sense for it to take 25 days, as you would only have learned 5 archetype abilities by level 5 of Kensai.

Not to mention that if you want to remove your old archetype, first you have to retrain out of Bladebound, which modifies one ability and replaces another, for a an additional of 10 days. But that's not required, as both archetypes are compatible.