I'm working on a burn out house, it has a 200amp service on it, the owner has added so many new things to the home including a 3 story addition, that I'm having to upgrade to a 400 amp service.
The inspector said it had to be a side by side set up, the existing 200 amp service is in such a location that it won't allow this set up, the inspector said I could use the 200 amp panel as a junction box,,
How do I do this,, do I just wire nut all the wires in the 200 amp panel and run through conduit to new double 200 amp panel or do I use one subfeed wore to the old panel and leave the breakers,, and if I leave the breakers,, Ill still have new breakers in the side by side service,, the reason for the conduit is that this is all outside and the side by side 400 amp service will be about 6 feet away from the 200 amp service,,

If it were me, I'd check to see if the following solution would be allowed. I think your very worried about things looking very messy, so lets use an industrial technique.

1. Terminate all wires in labeled DIN terminals mounted on DIN rail. You can get terminals rated in all different ampacities. You can get ground blocks too.
2. Run THNN/THWN of the proper gage to the new panel, making sure to observe any rules about number of wires allowed in the conduit or conduits.
3. Get breaker cover plates for the old panel.
4. Label the individual wires going from the "junction box" to the new panel. For all intents and purposes they can be labeled sequentually.
5. You could use ground DIN terminals. They are green and yellow.
6. I'd ground the panel to the house ground rod and I'd doubt that you would have to run separate grounds to the new panel.
7. If you have access to a label maker, you could use PP1-1, PP1-2 etc, as labels on the wires.
8. Label the panel as a junction Box.
9. Mark the last used number inside the panel.

This will give you a very clean installation without a rats nest of wires.