Exactly - the exchange power overhauls are a great example of behind-the-scenes work. Not only having to up-lift the mains feeds and all it's associated work, but the fact that the stand-by generator (Engine set) may also have to be swopped out as well ?? This is a mahoooosive task.
Regarding your pole/chamber (joint box) question - it all depends on the original infrastructure and how 'fluid' it s, as to how they would approach the FTTP task ??
For example, the pole feed cable may be 'Direct in ground' (DiG) cable, this is an wire-armoured cable that does what it says on the tin, it just sits in the ground and isn't fed through a duct. If this was the case, new duct-work would be provided.
Conversley, if yours goes under a road, it most probably will be ducted to the pole-bottom, so yes ... we would have the lads test rod the section and mark up where the stoppage is, and then have it dug and a box put on it.
Poles being replaced is a totally different question though. They could be classed by our pole testers as D-Poles (Dangerous), or they may be to short to carry the flying overhead wires at the now required heights, that would have been different when the poles were originally installed ??
Also on our builds, you may notice completely new poles going up to provide out new FTTP infrastructure. Our remit is to follow the original copper route, however, sometimes it just isn't cost effective and so the lads will notice the local authorities of their intention to provide a pole and place a stake in the ground on-site with a written version of our intent ... in order to give the local residents the chance to contest it.
That's why I love my job, the challenges are similar but unique to every area - veeeeery stressful but rewarding.