So, when we play in different formations during the same game, which is normal for us, and for most teams, that's a Plan B because the formation rules the tactics?
That makes no sense. By your definition all clubs then are using Plan A, B, C and probably D every match. Which would make your point moot because it's a tautology.
The formation is not the same as the tactics.
Our players are constantly doing various things during matches depending on different situations. That doesn't mean they're not playing within the same basic philosophy. I think you don't really understand what Pochettino actually means by tactics, or what he asks the players to do. You still haven't given an example of when our tactics changed this year. They factually haven't.