If it ain’t broke, don’t fix it!
And whipping with thread is far from broke!
The companies don’t make general run of the mill rods to be repaired, they make them as cheap throwaway articles. Made with the cheapest for them, parts, to sell at the maximum mark up they can get for them. Try getting a replacement section 2 years on for a rod of this type after they’ve launched their next super duper model, you’ll be very lucky indeed if you do.
All the points made so far about how do you get a replacement tube over existing rigs on the section are well made, you don’t, it is that simple.
As someone who has repaired/made many rods for myself and other people since 1969, you’d be surprised how many rings get damaged and have to be replaced. More so now with anglers not stripping the rods down and packing away in protection tubes to minimise accidental damage.
The problem is, assuming it is a problem, that to bend the rod in a natural curve via the line going to the bait and any hooked fish it needs rings on the rod that have to be fixed on the blank in someway. And now and again a ring may need changing because it gets damaged/broken. Most if not all of the modern insert rings, the inserts are glued in and any bang on the metal housing will and does break the bond between the two parts, the inset invariably getting lost before the owner realises it. A repair if you have the insert can be carried out, but in my experience eventually fails in about 60% of the repairs, even when you use the so-called best types of glues. Facilitating the fitting of a new ring with matching coloured fitting material(s) be that whipping thread or shrink tube type material.
I, nor have any of the specialist rod builders I have ever spoken to, have come across anything that is as durable or practical as whipping thread as an initial fixing material for rod rings.
Yes it not a process that everybody can do and it takes time to learn and do neatly, but done properly it is in my view a thing of beauty!
So no it isn’t broke and it doesn’t need fixing, it just needs learning to do it via practice, to make it perfect.