According to Canon, this god is dead, however, a sect within the Lathanderite Church known as the Risen Sun Heresy, preaching that Lathander is about to be reborn as Amaunator.

I am asking that if a Lawful Neutral cleric of this sect could exist but still have Lathander as his prime deity (Who he believes is about to turn into Amaunator.)

Would the Risen Sun Heresy be good aligned?

Would I need to App to be part of this Heresy?

Amaunator was 'THE' Deity of Law and order, bureaucracy and such, and such is neither inherently good or evil, if it is possible to be LN cleric of the Risen Sun Heresy, I would be glad!

Also, would they act like Lathanderites, or Amaunatorans? (Who were lawful to the extreme)

Edit: Please don't post in other people's DM Q&A Thread.

He would probably NOT be a cleric. As I suspect, Lathander does not grant spells to heretics but I could be wrong.

Would the Risen Sun Heresy be good aligned?

Would I need to App to be part of this Heresy?

Lathander grants spells unless we decide he doesn't. I can't say if we have an official stance on this yet. Personally, I think I'd go with an Amaunatori cleric who focuses on the Lathander/Amaunator relationship rather than a Lathanderite cleric who is really more an Amaunatori. Amaunatori clergy members are generally more prone towards neutral and evil; you can be whatever, as Mort said, but should probably at least be lawful and prepared to suffer some evil points. I would also suggest applying, if only so as to make sure that DMs and players agree on the interpretations.