Here is a copy of the law:
(a) A person who—
(1) knowingly removes, obliterates, tampers with, or alters an identification number for a motor vehicle or motor vehicle part; or
(2) with intent to further the theft of a motor vehicle, knowingly removes, obliterates, tampers with, or alters a decal or device affixed to a motor vehicle pursuant to the Motor Vehicle Theft Prevention Act,
shall be fined under this title, imprisoned not more than 5 years, or both.
(b)
(1) Subsection (a) of this section does not apply to a removal, obliteration, tampering, or alteration by a person specified in paragraph (2) of this subsection (unless such person knows that the vehicle or part involved is stolen).
(2) The persons referred to in paragraph (1) of this subsection are—
(A) a motor vehicle scrap processor or a motor vehicle demolisher who complies with applicable State law with respect to such vehicle or part;
(B) a person who repairs such vehicle or part, if the removal, obliteration, tampering, or alteration is reasonably necessary for the repair;
(C) a person who restores or replaces an identification number for such vehicle or part in accordance with applicable State law; and
(D) a person who removes, obliterates, tampers with, or alters a decal or device affixed to a motor vehicle pursuant to the Motor Vehicle Theft Prevention Act, if that person is the owner of the motor vehicle, or is authorized to remove, obliterate, tamper with or alter the decal or device by—
(i) the owner or his authorized agent;
(ii) applicable State or local law; or
(iii) regulations promulgated by the Attorney General to implement the Motor Vehicle Theft Prevention Act.
I've added the bold to make it stand out. Pretty clear it's not illegal to remove the VIN plate and restore it if you are the owner, or the restorer and it's reasonably neccessary.
