You can put the serial number anywhere on the receiver that you like, however, you cannot remove the original one! If you cover it in some way you must be able to remove the covering so that its visible (can be checked).
Under Section 108 of the Criminal Code.
Tampering with serial number
108. (1) Every person commits an offence who, without lawful excuse, the proof of which lies on the person,
(a) alters, defaces or removes a serial number on a firearm; or
(b) possesses a firearm knowing that the serial number on it has been altered, defaced or removed.
Punishment
(2) Every person who commits an offence under subsection (1)
(a) is guilty of an indictable offence and liable to imprisonment for a term not exceeding five years; or
(b) is guilty of an offence punishable on summary conviction.
Exception
(3) No person is guilty of an offence under paragraph (1)(b) by reason only of possessing a firearm the serial number on which has been altered, defaced or removed, where that serial number has been replaced and a registration certificate in respect of the firearm has been issued setting out a new serial number for the firearm.
Evidence
(4) In proceedings for an offence under subsection (1), evidence that a person possesses a firearm the serial number on which has been wholly or partially obliterated otherwise than through normal use over time is, in the absence of evidence to the contrary, proof that the person possesses the firearm knowing that the serial number on it has been altered, defaced or removed.
R.S., 1985, c. C-46, s. 108; 1991, c. 40, s. 20; 1995, c. 39, s. 139.
