Let $A$ be a matrix with real eigenvalues, its maximum eigenvalue is $0$ and it has sum for rows equals to zero. Let $B$ be a matrix $\mathrm{diag}([1\,0\, ...\, 0])$ and let $I$ be the identity matrix. Then $\lambda_{\max}(A+B)\neq\lambda_{\max}(A+I)=1$ ?
The last equality is from $\lambda(A+I)=\lambda(A)+1$.