Replacing site

[bcp]

Good Afternoon,

I have two questions that are similar.

Website #1 is a using an ithemes template. I would like to upload genesis and use Freelance. However it needs a bit of customization. Can I do that offline and then replace the current site making sure everything fits and works?

Website #2 is a Thesis blog site. So the same question. The only thing different here is that I will be importing content from an existing (non-WP)bmembership site and will be adding Wishlist Member. I can import the other content after the changes are made if necessary (it's hosted differently).

I understand there is something that I can use to create the site locally and then upload the whole thing easily. Is this true?

If not, or if it's complicated for someone who has not done this or very time consuming please let me know that as well. I'm not opposed to trying to find someone to do this.

Thanks.