Roof bars have been a bone of contention with owners both on ZS but particularly the original MG5 and a keyword here appeared to be "Approved". Look back over the MG5 comments on this forum (and others I suspect) and the Podcasts and you'll find that MG had an issue with the "Approval" of the bars and their designation as "Decorative" in the UK market. Under pressure from owners and probably dealers on behalf of prospective owners and owners who had mistakenly assumed that the roof bars were functional, MG sort retrospective "Approval" and issued an amendment to the MG5 Owners Manual Approving the Bars for load carrying. Approval carries more weight (excuse the pun) than owners might wish to believe.
When a vehicle is sold it is legally sold to be safely used for certain purposes and this is why Tow Bars have limits or none at all. For example, the 2019 ZS EV is not Approved for towing even though the ICE ZS with the same chassis is approved as crazy as this seems when the EV version has a higher kerb weight and more torque than the ICE stablemate - why you might ask? the answer with the MG5 SR is that MG didn't subject its roof bars to "Type Approval Testing" before offering the car for sale apparently. MG did subsequently submit the car for testing and that is why the amendment was subsequently issued and Facelift MG5 and the Trophy MG4 are approved for roof bar loads. I would venture to suspect that MG did not submit separately for Type Approval the ZS SE roof carrying capacity using unknown 3rd party products. I suspect that this would have been a lengthy and expensive process for the UK market when customers had an alternative model they could buy if that was important to them.
So does this matter? Unfortunately yes, quite apart from MG's stance on your warranty, "Non-Approved" parts and use can have consequences both legally and financially particularly if there is an accident. In effect, you could find yourself before the law for "Overloading" your vehicle and therefore be driving an unsafe vehicle on the public highway. This might be just the reason for your insurance to be considered "invalid" and so meaning you have been driving without insurance. The same could also be said about fitting tyres with different sizes or lower load/speed ratings than specified in the manual ie Approved.