Is the wiring kit / harness and bypass relay mandatory when connecting a tow bar on an Octavia MKII 2012?

I am looking at fitting a towbar for a small trailer and bike carrier. I therefore "simply" need to get brake / reverse lights and indicators.
My car has no reversing sensors or camera and I can very much do without having a warning sign on the dashboard to remind me I am towing something.

=> Back in the old days, it was just a question of splitting a couple of cables in the boot and job was done. What happens if the same is done on the Octavia? Does it detects something is abnormal and generates an error?
Given my basic needs, I would rather avoid the expense and complexity of fitting the full wiring harness if i can avoid it...

Thanks for your clarification!