A Unity3D editor script to add reset buttons to the transform inspector and Vector3 copy paste functionality.Add it to a folder called Editor in your project to use it.

Inspector_Transform.cs

using UnityEngine;
using UnityEditor;

/// <summary>
/// Adds reset buttons to transforms to quickly reset position, rotation and scale to default values
/// Features:
/// - Copy and paste values in another transform by clicking on a label (E.G. Position) and using CTR+C CTRL+V
/// </summary>
[CustomEditor( typeof( Transform ) )]
public class Inspector_Transform : Editor
{
    public override void OnInspectorGUI()
    {
        Transform t = (Transform)target;
        Undo.RecordObject( t, "Transform Change" );

        Vector3 p = t.localPosition;
        Vector3 r = t.localEulerAngles;
        Vector3 s = t.localScale;

        // Position
        EditorGUILayout.BeginHorizontal();
        {
            if( GUILayout.Button( "0", GUILayout.Width( 20 ) ) )
                t.localPosition = Vector3.zero;
            GUI.SetNextControlName( "Position" );
            p = EditorGUILayout.Vector3Field( "Position", t.localPosition );

            CopyPaste( "Position", ref p );
        }
        EditorGUILayout.EndHorizontal();

        // Rotation
        EditorGUILayout.BeginHorizontal();
        {
            if( GUILayout.Button( "0", GUILayout.Width( 20 ) ) )
                t.localEulerAngles = Vector3.zero;
            GUI.SetNextControlName( "Rotation" );
            r = EditorGUILayout.Vector3Field( "Rotation", t.localEulerAngles );

            CopyPaste( "Rotation", ref r );
        }
        EditorGUILayout.EndHorizontal();

        // Scale
        EditorGUILayout.BeginHorizontal();
        {
            // Float field for uniform scale
            float uniScale = (t.localScale == (Vector3.one * t.localScale.x)) ? t.localScale.x : 0.0f;
            EditorGUI.BeginChangeCheck();
            //if( GUILayout.Button( "1", GUILayout.Width( 20 ) ) ) // Comment this out if you want a button to reset scale to 1
            //    uniScale = 1.0f;
            uniScale = EditorGUILayout.FloatField( uniScale, GUILayout.Width( 20 ) );
            if( EditorGUI.EndChangeCheck() )
                t.localScale = Vector3.one * uniScale;
            GUI.SetNextControlName( "Scale" );
            s = EditorGUILayout.Vector3Field( "Scale", t.localScale );

            CopyPaste( "Scale", ref s );
        }
        EditorGUILayout.EndHorizontal();

        if( GUI.changed )
        {
            t.localPosition = p;
            t.localEulerAngles = r;
            t.localScale = s;
        }
    }

    void CopyPaste( string controlName, ref Vector3 v3 )
    {
        if( Event.current.isKey == false || GUI.GetNameOfFocusedControl() != controlName )
            return;

        if( Event.current.control && Event.current.keyCode == KeyCode.C )
        {
            EditorGUIUtility.systemCopyBuffer = JsonUtility.ToJson( v3 );
            GUI.changed = true;
        }
        else if( Event.current.control && Event.current.keyCode == KeyCode.V )
        {
            v3 = JsonUtility.FromJson<Vector3>( EditorGUIUtility.systemCopyBuffer );
            GUI.changed = true;
        }
    }
}