Can be used to roleblock offensive Herrscher roles?
If you already know they are Herrscher, they should be lynched. There are some cases where it may be good to use as town (an extremely likely Herrscher doesn't get lynched), but I will not advocate its use.
Can be beneficial for town as long as it doesn't coincide with Durandal target. Yae should out a list of targets here and Durandal investigates outside of it.
This sounds like a bad plan. All the targets will be immune to Fu Hua, allowing mafia a choice of guaranteed NKs. Raiden Mei takes priority and could potentially move the NK elsewhere (including Herrscher), but you would effectively be nullifying Fu Hua.
Both can be Herrscher.
As I mentioned before, subtle things. Like not forcing Durandal to counterclaim if someone thinks a fake Durandal claim will save them from getting lynched, but having Emma Planck do it. If you need to choose between lynching one of two people of unknown alignment, of which one has a role that is really useful to town if they are town, you choose the other.
I disagree; if someone claims, Cocolia can verify this. only concern would be a fake or maf Cocolia.
I'm not saying the information is useless, I am saying you do not need tips on ability usage for an ability that is passive.
There's also some theorycrafting I've done: if Emma Planck finds someone's role, and Theresa determines that person's ability type and it doesn't match with what their role is, they're confirmed Herrscher. It can't confirm someone as town, but it can confirm if they have a Honkai core.
That's basically what I was saying on Theresa. You do not even need Emma Planck for this. As long as people are truthful about their role claims, anyone that has claimed will be a viable target. That's one of the reasons I'm being so insistent on truthful role claims.