Hi, so I have been trying this for about 2 hours and I just wanted to share this here because I did not find anything at all on the internet regarding this specific mechanic, so I hope this will help someone in the future.

I was having problems on quickly attaching and detaching from the rope, because if you do it normally, you can't just detach straight after attaching as there is a cooldown on the action. What I did not realise is that when you jump while attached, the rope "pushes" you away from it, detaching you. So when people do the Icebox rope boost jump (which is still possible in patch 6.03, as I just did it) what they never say is that you need to jump -> attach when at the highest -> JUMP AGAIN (mid air) -> rope pushes you forward. So you don't press the "use" button (default F) twice, but only once to attach to the rope.

Again, attach-detach fast is not possible, because there is a cooldown, so instead of detaching, you need to jump out of the rope.