CSA is a double edge sword. Most manufacturers can’t bost this, when a modification happens afterwards. A new on-site electrical approval is required. This is why under the CSA they cut off the cord so a second approval is required on site. This makes a second certification under the CSA and governing law . Homeowners are allowed to apply for this... and so are electricians with a third-party inspection. But in anyway if this is a residential property, the ESA needs to be involved. If it is a commercial property, a commercial/industrial electrician is allowed to sign off for it if he is licensed appropriately, which has no residents . There is no if and or butts!
Sounds like maybe you missed the point....? Some products are complete, needing only to be plugged-in, some are parts used in a larger product or system, and some, like an RPC, are "installed" and the installation matters.
That is what the NEC is for in the US. UL is a required approval for the piece, be it RPC, an electrical box, wire, a conduit connector, etc, but a separate inspector looks at the installation. There is no "cutting off the cord", it is just another level of inspection. The part or incomplete unit has "recognition", but not a full approval, because more has to be done to it.
In this case, the RPC as a unit would receive a form of UL (or in this case presumably CSA) approval/recognition, to assure that it is worthy to be installed. Then the electrical inspector would check to be sure that the thing was installed in accordance with its requirements etc, per the NEC. (National Electrical Code), AKA NFPA 79, as accepted by the local authorities.
The electrical inspector has nothing to do whatever with the innards of the thing, he just looks at the UL mark to be sure it is "listed for the use", and the marked ratings to be sure that appropriate wire is used to connect it, etc.
For parts a manufacturer uses in a product, periodic inspections by UL (and presumably CSA for you) assure that the parts called for and documented to be the same as the ones used in the test samples are actually being put in the product.
The approval mark is no double-edge sword, it is the proof that the item has been inspected and tested to be safe per the regulations when installed correctly. Without that, an OSHA inspector in the US can (and I have seen it done) close down the place until non-approved equipment is disconnected. The NEC here, and presumably the Canadian equivalent, calls for equipment to be "listed for the usage", generally meaning tested to UL standards for the use it is intended for. The mark is intended to prove that, and to permit that usage.
Obviously if equipment has been modified in ways outside what is listed in instructions for use, then the UL mark no longer applies. Likewise if not used "as intended". But that is not what is in question here.