Yes I tested this, initally I had wrong quaternions with that :
quat.x = cy * sr * cp - sy * cr * sp
quat.y = cy * cr * sp + sy * sr * cp
Then I done some inversions and it worked
quat.x = cy * sp * cr - sy * cp * sr
quat.y = cy * cp * sr + sy * sp * cr
I successfuly produced valid mapeditor files then I converted them to ymap using a tool and it worked like a charm.