"and this skill is always a class skill for you" – "always" does it have any meaning in Pathfinder?

This word is only there because some rules have been changed between 3.5 and Pathfinder, such as class skills work and how multiclassing works, and they had to specify that the skill is a class skill, regardless of your class. This has no effect, if a skill is a class skill, it is a class skill regardless of your courses and other mechanics, and no mechanic allows it. do not to be a class skill for you.

However, there are archetypes that change your class skills for this class, and saying that this always counting as a class skill should avoid a possible removal of an archetype. There are many examples, but to name one, the Urban Bloodrager removes certain skills from their list of class skills:

Classroom skills: Urban stew adds the following diplomas: Diplomacy (Cha), Knowledge (Local) (Int), Linguistics (Int) and Profession (Wis), and eliminates the animal to handle (Cha), knowledge (nature) (Int) and survival (Wis).