Charges $+q,+q,-q,-q$ are placed at the vertices $A,B,C,D$ of a square respectively. Let $\vec{E}$ be the electric field and $V$ the potential at the centre. If the charges on $A$ and $B$ are interchanged with those on $D$ and $C$ respectively, then:

Potential ($V$): $V$ is a scalar quantity. $V=\sum \frac{1}{4\pi {ϵ}_0}\frac{q_i}{r}$. Since all vertices are at the same distance $r$ from the center, $V\propto (q_A+q_B+q_C+q_D)$. Interchanging positions does not change the sum of the charges. Thus, $V$ remains unchanged.Electric Field ($\vec{E}$): $\vec{E}$ is a vector quantity. The field at the center is the vector sum of fields from each charge. Initially, $+q$ charges at top and $-q$ at bottom create a net downward field. After swapping, $-q$ are at top and $+q$ at bottom, creating a net upward field. The direction of $\vec{E}$ changes.