I don't think (Guided) is a MOD. It doesn't modify a normal BS Attack, rather it allows you to perform a different kind of BS Attack. If it was a MOD which applied to all the owning trooper's BS Attacks, then a missile bot could never take a normal shot with LoF at a unit that wasn't Targeted, because its BS Attack would be MODded to only work against troopers in the Targeted state. Consequently, I don't think that Speculative Attack is affected by a trooper having the BS Attack (Guided) skill, just as a normal BS Attack isn't affected by the trooper having the BS Attack (Guided) skill.
I think the reasoning is sound. BS Attack (Guided) is written as a modifier to BS Attack and even if that comes with a bunch of extra rules, like Immunity does, you are still declaring the actual skill "BS Attack" as opposed to performing a BS Attack that is a component of a different skill. I mean... the net effect isn't all that huge. Regular Guided: Short skill at flat BS value centred on the target. Able to use any of the BS weapons from panoplies. Speculative Guided: Entire Order skill at flat BS value off-centre on the target. Unable to use any of the BS weapons from panoplies.
