How can i flip the direction of the Triangles within a quad?
delete the edge in quad face and redo the 2 triangles the way you want it
just curious why do you need that ?
You can also select the edge and use the command: edge > rotate edge CW or CCW
For several reasons. One is how light reflects on low poly surfaces. Another is to help with better deformations. Also helpful if you need a concave quad instad of convex.
Not that simple. First you have to triangulate the quad (Strg+T), then rotate edge CW or CCW and finally rejoin the triangles to a quad again (Strg+J). Found an old article on blenderartists about it.