Earlier quoted context omitted.
Technically, IMSI is not a device identifier. MT has IMEI and SIM (or more precisely ICC) has ICCID (which is normally never transmitted over the network). And the legislation probably specifically targets spoofing the IMEI, as spoofing IMSI does not gain you anything other than absence of service (on normal GSM/3GPP network).
The fact the Government is using it as an identifier likely means they can argue legally you are attempting to change the identifier. Technically correct for technical discussions is not the same as contextually correct in a court room.
From legal standpoint, device that spams IMSI catcher with registrations with random IMSIs is mostly same thing as the IMSI catcher itself, ie. device that requires it's own broadcast license to operate, as such device certainly does not meet legal (and technical) requirements for it to be an cellular phone.
On the other hand, generating random IMSI, burning that into ICC and thus producing unusable SIM is probably perfectly legal even when you put that inside normal GSM phone (from network standpoint it will behave mostly same as phone without any SIM). In practice SIMs with completely made-up IMSIs are even commercially available (idea there is that some phones will not fully boot without SIM).