How to compute the change in vector when it's referential vector changes?

Hello,

Let's say that I have Vector A and then two other (sub-ordinate) Vectors B & C. When Vector A changes, I wish B and C also to change in accordance. When I say in-accordance I mean like parent-child transformation.

PICTORIAL REPRESENTATION :

CODE :

I supply force to the rigidbodies. These forces are computed when the gravity is (0,-10,0). Now when I want to change the gravity to (10,0,0) what should be the force.

     // The required Force applied in Flap mode
     void FlapForce()
     {
         //HORIZONTAL FORCE
         if(!HNEXT)
         {
             rigidbody.AddRelativeForce((Vector3.right) * DeltaTime * LeftDrag * 3); 
             if(LeftDrag < 400)
                 LeftDrag += ToTarget(DefaultDrag,TurnSine);
             rigidbody.AddForce(2,(-LeftDrag/50),0);
         }
         
         if(HNEXT)
         {
             rigidbody.AddRelativeForce((-Vector3.right) * DeltaTime * RightDrag * 3);
             if(RightDrag < 400)
                 RightDrag += ToTarget(DefaultDrag, TurnSine);
             rigidbody.AddForce(-2,(-RightDrag/50),0);
         }
         
         //VERTICAL FORCE
         if(!VNEXT)
         { 
             rigidbody.AddRelativeForce((Vector3.forward) * DeltaTime * UpDrag * 3); 
             if(UpDrag < 400)  
                 UpDrag += ToTarget(DefaultDrag,TurnSine);
             rigidbody.AddForce(0, (-UpDrag/50),-2);
         }        
         if(VNEXT)
         {
             rigidbody.AddRelativeForce((-Vector3.forward) * DeltaTime * DownDrag * 3);
             if(DownDrag < 400) 
                 DownDrag += ToTarget(DefaultDrag, TurnSine);
             rigidbody.AddForce(0,(-DownDrag/50),2);
         }
     }

Please and Thank you,

How should I compute the forces in accordance to the changes in the gravity?

Karsnen.