Yeh just MIG welded on.
The reason I did this was because i bottomed out and damaged my flexi section. Went to my local Partco (they were very helpful), looked at the universal flexi's they sell and the only correct length they had was too wide, ie. once one was welded the second wouldn't be able to be fitted. They did however sell what you see in the pics. only problem is you have to buy 2 metres of the stuff! Think cost was about £12-14, but does the job very well. Simply cut / angle grind old flexi's off, cut your new piece's to length and I personally welded onto the original weld, due to more material being present, you don't want to be chasing holes
It is slightly stiffer than the original flexi's but less prone to being damaged.
I've since replaced it for an ansa (which has no flexi) and have not got a problem at road speeds with vibration, inless you are a very spirited driver
This just lives in the garage now acting as a spare with the manifold, if the ansa needs attention in the future
Like so many things, there's plenty of how-to guides that could be done, but would they be viewed / used
however big or small the job