Was there a court ruling or just RCMP interpretation? Because a -180 receiver isn't "designed" to be centerfire. The receiver has no bearing on whether or not the rifle is centerfire or rimfire, it is essentially just a chassis of sorts to house the internal components (these internal components being the parts that are actually designed around a specific rimfire or centerfire cartridge) and provide attachment points for the other parts of the firearm.
I could see them making the argument that the receiver is dual-use and must therefore default to the most restrictive ruleset (i.e. centerfire), but that leaves the question why dual-use pistol magazines aren't subject to the most restrictive interpretation as well. But that's all beside the point because dual-use isn't defined anywhere in Canadian firearms law.
In addition, nowhere in the law does it also differentiate between a rimfire firearm and a "rimfire firearm with a centerfire receiver". One of the criteria for a restricted firearm is being capable of discharging centerfire ammunition in a semi-auto manner; and if it fails to meet the definition of a restricted or prohibited firearm, it is therefore non-restricted unless prescribed by law. And non-restricted rimfire rifles have no barrel length requirements.
Personally, if I had a rimfire -180 variant, I'd throw on a short barrel and risk an ignorant cop. We do it all the time with other black rifles that can be easily misidentified. The law is very clear and it is on our side, in my opinion.
