You can use a script and change the rotation to 0 for all that are not zero.

mark-y: yes, but i have lot of such clips and change manually is not ideal.

jetdv: what would be that script exactly? :)

@relaxvideo

@mark-y

In addition to what mark-y said, you can select one or more media clips in the Project Media panel and then R click, select properties, then select one of the rotation options so your clips display the way you want. That will affect all the media clips you have selected.

Thank you @Robert Johnston

@relaxvideo You asked about changing the metadata, sorry I misunderstood your intent. That said, the solution to your undelying question is quite easy to do with one click ---

Here's where I first referenced Rotation in the tutorials

You can try this script and see if it does what you want:
 

using System;
using System.Collections.Generic;
using System.Collections;
using System.IO;
using System.Text;
using System.Windows.Forms;
using System.Globalization;
using System.Drawing;
using System.Runtime;
using System.Xml;
using ScriptPortal.Vegas;

namespace Test_Script
{
    public class Class1
    {
        public Vegas myVegas;

        public void Main(Vegas vegas)
        {
            myVegas = vegas;

            foreach (Track myTrack in myVegas.Project.Tracks)
            {
                if (myTrack.IsVideo())
                {
                    foreach (TrackEvent evnt in myTrack.Events)
                    {
                        VideoEvent vEvnt = (VideoEvent)evnt;
                        VideoStream vs = (VideoStream)vEvnt.ActiveTake.Media.Streams.GetItemByMediaType(MediaType.Video, vEvnt.ActiveTake.StreamIndex);
                        vs.Rotation = VideoOutputRotation.None;
                    }
                }
            }
        }
    }
}

public class EntryPoint
{
    public void FromVegas(Vegas vegas)
    {
        Test_Script.Class1 test = new Test_Script.Class1();
        test.Main(vegas);
    }
}