If the EE is a PE(professional Engineer) can't he sign off on the change and supercede code
No, an engineer can not change the adopted code.
What you may be thinking of is this.
310.15 Ampacities for Conductors Rated 0–2000 Volts.
(A) General.
(1) Tables or Engineering Supervision.
Ampacities for conductors shall be permitted to be determined by tables or under engineering supervision, as provided in 310.15(B) and (C).
Under engineering supervision ampacities may be different than the NEC tables.
