[PF] Tinkering with class-based enemies

[Dust]

This should be a pretty straightforward question, but I'm a new GM to pathfinder and want to double-check this before I seriously hazard the character life expectancy of my group.

If I'm dealing with a pre-made adventure path and want to re-write several NPCs (which show up as major adversaries) does changing their class generally affect the encounter's CR? What should be taking into consideration when doing this?
Specifically, I'm going to be converting NPCs in the Skull and Shackles adventure path, transforming Cap'n Barnabas Harrigan from a Fighter/Rogue to an Myrmidarch Magus, and the Hurricane King from a Fighter 8/Inner Sea Pirate 10 to a Stormborn Sorcerer/Master of Storms in order to drastically change the last few (fairly lackluster) modules.

Thanks in advance, guys.

[AttilaTheGeek]

According to the CR system, no, but according to the tier system, yes. I'd say go for it, but don't throw a bunch of save-or-sucks at your players. Nothing's fun like being Disintegrated and rolling a 1.

[Dust]

That was my thinking as well - I'm dealing with a solidly tier 3 party, so I don't feel as if I'd need to drop the pre-existing npcs levels down more than one or two, or just spend more of their equipment budget on behind-the-scenes pirate-y stuff as opposed to specialized combat gear.

[Dust]

With absolutely no expertise in making high-level pathfinder characters, this is what I came up with for the first of the two remakes. I feel that although his AC is low, Blink, Repulsion, and the defensive benefits from Elemental Body IV should keep melee characters struggling to land solid blows, and that this 16th level blaster sorcerer should be about on par with an 18th level gunslinging Fighter. He lacks Freedom of Movement and defensive casting, which is...I don't really know how essential that is, all things considering.

What are your thoughts on this remake? Remember, no system experience - I'm probably seriously over or under-estimating where numbers should be as a proper CR 18 encounter.

Kerdark Bonefist, the Hurricane King
Level 16 Human Stormborn Sorcerer

STR 12 (+1)
DEX 17 (+3)
CON 18 (+4)
INT 10 (+0)
WIS 12 (+1)
CHA 27 (+8)

HP 155
AC 25, (25) 21 FF, 32 when in elemental form
FORT 16/20 with greater heroism
REF 15/19 with greater heroism/22 with heroism + elemental body
WILL 18/22 with greater heroism
CMD 24/27 elemental body
CMB 9

CLASS FEATURES, FEATS AND TRAITS
+1 to save DC vs spells with [sonic] or[electrical] descriptor, Resist Electricity 5, Resist Sonic 5, +2 on saves vs all electrical, ignore the effects of weather, +2 on saves vs fear, brew potion, +1 dodge to AC, +2 on save difficulty vs evocation spells, +4 init, Spell specialization (Chain Lightning), Sorcerous Bloodstrike (Thunderbolt), +4 bonus on caster level checks to overcome spell resistance, Thunderbolt bloodline power 1/day

SPELLS
Spells per day: X/6/6/6/6/6/6/5/3
Known: 9/5/5/4/4/4/3/2/1

1 - Alarm, Comprehend Languages, Keep Watch, Interrogation, Snapdragon Fireworks, Shocking Grasp
2 - Fog Cloud, Create Treasure Map, Spell Gauge, Track Ship, Adoration, Gust of Wind
3 - Blood Biography, Illusory Script, Water Breathing Blink, Lightning Bolt
4 - Named Bullet, Mass Daze, Detect Scrying, River of Wind, Shout
5 - Black Spot, Lightning Arc, Communal Stoneskin, Unseen Crew, Overland Flight
6 - Repulsion, Legend Lore, Greater Dispel Magic, Chain Lightning
7 - Elemental Body IV, Spell Turning, Control Weather
8 - Moment of Prescience

EQUIPMENT
Golden Earrings of Alluring Charisma +6, Belt of Physical Belt +6 (DEX and CON), Bracers of Armor +8, Echoing Ectoplasmic Conduit Rod (multiple metamagic rods as single item), Ring of Protection +3, Orange Prism Ioun Stone, Ring of Mind Shielding, Cloak of Resistance +5, Pirate's Eye Patch, Potion of Greater Heroism, 5 bonus points of Skull and Shackles Plunder
Kerdak's stats also assume he is gaining the benefits of the Lord's Banner of Victory (+2 saves) on board his ship.

SUMMARY
Chain Lightning lets him 19d6 damage on an entire crew of enemy pirates. With a DC 27 for initial target and 25 for secondary targets, folks probably won't be succeeding on many reflex saves to halve.
An Unseen Crew will keep his ship functioning while battle rages so that he can dedicate his best half-dozen fighters - all buffed up with Stoneskin - to keeping the PCs on deck busy, and Moment of Prescience and Spell Turning should protect him from the first few save-or-lose.