Currently on ZC 1.5.5a and I am basically rebuilding from scratch and on another server a new version of the live site.
There is quite alot of junk in the old site, old plugins no longer needed etc, bad product images etc
So I thought it may be best to start afresh completely.

Now, If I do this, I obviously need to be able to copy over existing customers details, orders and any other relevant information so that when they log in there are no issues.
The products will still be the same, although the ID numbers may change due to some old products still on the live site.
If I was to copy over ALL the tables from the live site as a test first before I start building, how do I then just update new customers and their orders while I am building the new site?
If I recopy over again then it will just overwrite any SQL changes I have made?

Or am I better to copy over the live database to the test build, make the changes, copy the whole lot back and re-run the sql for the new plugins on the live site again?