matlab code to obtain thenew right hand side b of a linear equation after transforming the matrix A to another matrix

Solving linear equations Given a linear equation of the form Ax=b For example where A=[6 2 4;3 4 3; 3 1 2] and b=[26 19 13]' A =

     6     2     4
     3     4     3
     3     1     2
b =

    26
    19
    13
Case 1
The elements of A is multiplied by (-1) except the diagonal  elements to give matrix G=[6 -2 -4;-3 4 -3;-3 -1 2] and the new b denoted by c =[-2  -11 -1]'
G =

     6    -2    -4
    -3     4    -3
    -3    -1     2
c =

    -2
   -11
    -1
I need matlab code to transform matrix A to matrix G and vector b to vector c

Case 2 I want to form another linear equation which is A’x=k how do I obtain my k from b after finding the transpose of A. A'= 6 3 3 2 4 1 4 3 2