How to approximate several variable irreducible functions to reducible

Question

$f:\{-1,1\}^n \rightarrow R$ with $f(x_1,x_2,x_3,\cdots,x_n)$ is any $d$ degree polynomial and irreducible then how to approximate $f$ to $g$ such that $g$ is reducible with distance between $f$ and $g$ is less. if it is not possible solution for at least $2$ degree polynomials.