Developing my site/changing my theme on a separate domain

Hi,

So i’ve got a pretty big site that I need to change the theme on. This is going to take me quite a while, as the current theme I’m using is not compatible with the new theme. I’ve got about 100 pages that uses a template on the current theme that does not exist on the new theme, which will have to be manually reposted on the new theme as they disappear when I change the theme.

To do this, I’m thinking of copying the entire current site to another domain that I own but don’t use for anything at the moment, rebuild the site there, and once done I will move that wp-installation over to replace the site on my current “active” domain.

My question then is: if I check the “discourage search engines from indexing this site” option on the new domain while i rebuild the site there, will I be in the clear of running any risk of screwing up any SEO up in terms of duplicate content and so forth? Or do I need to do anything more in order to avoid this?