How to align multiple callout titles?

Each layer will need it's own expression and will angle itself based on the anchor point of the layer.  

This line:

[radiansToDegrees(a),radiansToDegrees(b),radiansToDegrees(c)]

lists the three angles.  (not sure if you're saying you want to make a change here.)

Just underneath that:

}catch(err){
value
}

tells AE to use the orientation value if something is messed up.

To control when the expression is running, simplest option is to add a checkbox to the layer then add it to the main expression like this:

if (effect("Checkbox Control")("Checkbox")==1) {
	
try{
L = thisComp.activeCamera;
u = fromWorldVec(L.toWorldVec([1,0,0]));
v = fromWorldVec(L.toWorldVec([0,1,0]));
w = normalize(fromWorldVec(L.toWorldVec([0,0,1])));

sinb = clamp(w[0],-1,1);
b = Math.asin(sinb);
cosb = Math.cos(b);
if (Math.abs(cosb) > .0005){
c = -Math.atan2(v[0],u[0]);
a = -Math.atan2(w[1],w[2]);
}else{
a = (sinb < 0 ? -1 : 1)*Math.atan2(u[1],v[1]);
c = 0;
}
[radiansToDegrees(a),radiansToDegrees(b),radiansToDegrees(c)]
}catch(err){
value
}
} else {
	value
}

So when the checkbox is checked, run the expression, but if not, use the orientation value.