Immunity (ARM) and Immunity (BTS) state: Any Ammunition that requires a Saving Roll using the ARM/BTS Attribute is treated as Normal (N) Ammunition. Its special effects, and any MODs to the Attribute and number of the Saving Rolls are ignored. If the Weapon, Skill, or piece of Equipment used in the Attack has Traits, the Trooper is completely immune to any of those Traits that cause States, refer to inflicting Wounds, or reduce the Attributes of the target. For example, State: Dead, Continuous Damage, or ARM=0. Do Immunity skills, such as Immunity (ARM) allow troopers to ignore the modifiers to the saving roll imposed by Mods such as PS=X or SR-Y? For example, does this mean that a CC attack made with a CCW hitting a trooper with a relevant immunity always hits at PS8? Similarly, are armour saves made against a TAG's HMG made against an Immunity (ARM) trooper made at PS5? This seems like a major oversight in the transition to damage resolution, and I think clarification and errata is necessary.
Troopers with immunity dont ignore those skills effects, as you noted, only ammunition effects are ignored.
The second sentence is referencing the first sentence. "It's special effects" refers to Ammunition that requires a Saving Roll using the ARM/BTS Attribute and any MODs to the Attribute is referring to the affected Attribute in the brackets of the skill in question (e.g. Immunity (ARM) or Immunity (BTS)). PS is not a part of either of these clauses, so MODs to PS aren't affected by Immunity.
