How to set tag for gameobject created by VectorLine in runtime?

how to set a tag to the gameboject which created by VectorLine(using Vectorsity 1.4.2) before adding it into Hierarchy.

I presume you used the Instantiate function to spawn the object?
if so then your code should look like this:

JS

var prefab: GameObject;

function SpawnObject()
{
	var obj = Instantiate(prefab, transform.position, Quaternion.identity);
	obj.gameObject.tag = "MainCamera";
}

C#

public GameObject prefab;

void SpawnObject()
{
	GameObject obj = (GameObject) Instantiate(prefab, transform.position, Quaternion.identity);
	obj.tag = "MainCamera";
}

And if you want to change the tag before spawning it you should change the prefab tag.

prefab.tag = "MainCamera";

Also make sure to assign the prefab in the inspector.

You can use vectorObject.

vectorline.vectorObject.gameObject.tag = "theTag";