Actually, Book 3 assumes the players go into the event knowing its a trap (or suspecting it is), thus preparing for it. Glamored Armor, Hats of Disguise(Greater or not), and the like will all help with allowing even heavily armored PCs to look like they're dressed up.
Book 3 is probably the most linear of the books, but book 4 is no where near as such. Any of the targets in book 4 can be attacked in any order - except for the final target, as thats the hardest nutshell to crack and is basically the last target.
As for book 3... linear it may be, but its still got some VERY interesting encounters. Richard Pett is one of my favorite adventure Authors, ever since playing through his "The Wormwood Mutiny" Adventure at the beginning of Skull and Shackles.
Personally - nothing against Richard Pett. He is a great writer, but he is the same guy who thought CR3 tiny flying D6 bleeding mosquito swarms was a great idea to use as random monsters against level 3 characters in Skulls and Shackles - just check the obituary thread back there for some of the consequences of Mr. Pett thinking something is a "fair encounter" ....
Yes that is a very nasty situation the players are expected to put their head into. Hats of disguise - probably useless, perfect armour for that job... have it on time and be aware that it is needed ? Nevermind dancing with a two handed sword strapped to your back. Or a brace of pistols - disguised or not.
As for the Iron Willed "Stormtroopers of Cheliax" (ahem Kintargo)... yeah enough said..... Problem is... the only way to play this campaign reliably with magic as an effective suggestive means "as written" is building cheesy concepts.
Looking at it from a historic perspective... a lawful evil regime usually fared better if their servants and ruled are not Iron Willed and individualistic in their mindset, but meek followers who rather follow any rules dictated to them instead of standing up for their own vision of things. Lawful evil likes "broken" followers...
Something I also found odd... no Hellknights in the first Act ?