After rough-wiring my old house to a new 200 amp Main Panel (wired-in but not yet connected to the service line and still using the original 100 amp fuse-type panel) I've decided to build a major addition that makes the originally planned service entrance a poor location.

Question:
Can I install another new 200 amp main panel and service entrance (in the addition in a better location) and use the "first" 200 amp panel as a sub panel?
Or can/should I run approx. 40 feet of entrance cable from the "revised" meter to the original 200 amp main panel location?
Or should I un-wired the first main panel and extended all my home runs to a "relocated" new main panel in the addition?

I know I should have planned better... but I just got married... thanks for the help!

Personally I would have all in 1 Panel, considering cost and time.
No problem with 2 panels, could save a lot of work.
If you are able to leave the first where it is, why not just run new stuff from there,
Maybe 60 or 100? Amp breaker to feed to addition SubPanel.

The problem with installing a new 200 amp panel, is that it will not accept another 200 amp breaker to feed the existing panel. The existing panel may be only fed by possibly a 100 or a125 amp breaker. If this works for your ,then fine, no problem. Just remember to use 4 wire service entrance cable to feed the existing panel once the first main breaker is at the relocated service entrance.

If you do turn you first panel installed into a sub-panel make sure to separate the neutrals and grounds