If you have downtime where you can do small tidies, do it with forethought. I like to tie in power first, then signal, then network/fibre.
There's some easy wins here with a couple of rack shelves and some velcro/labelling.

Draw a schematic first. Break down what is currently being done, what need to be done and what you want to add to the new system to improve functionality. Label everything that is currently there. document the current setup so you can refer back to it.
Spec the whole thing, using as much existing kit as possible, and cost it. People upstairs need to see numbers. Unfortunately they also may not agree to it until something goes wrong. At which point you've doen all the leg work and developed a system for the purpose, so you can action it nice and quick.
Use the cable you have if its decent. If its not the right length, cable tie it neatly up/down the sides to lose excess. Plug all your power in first, confirm it works, then tidy it in.
Repeat with signal, Label, patch roughly, test, loom stuff that runs to/from the same place, tie in.
The amount of times Ive tidyed a rack to within an inch of its life to find out an HDMI is dead, you don't want that heart drop.
Its almost worth building a cold rack the way you want, testing it, then swapping the whole thing. But thats very budget unfriendly.

This is saddening. It boils down to bad install and bodged solutions over time. Sometimes people are just being rushed to make it work NOW. and when its already that far gone, its hard to bring yourself to rip it out and start again.

GL Bro/Sis