It seems to me the best way to approach this would be to use a sub-domain (something like “dev.yourdomain.tld”?) and install your WordPress installation in that directory.
That way, it will run from the “base” directory of the domain, so you can tweak you permalink structure until you are happy with it, and not have to worry about twiddling about with re-write rules that may have to change when the site goes live.
When all is the way you like it, just rename the “yourdomain.tld” directory to something else, then rename the dev.yourdomain.tld to “yourdomain.tld” and you are "good to go; in the meantime, both sites are fully available from a browser.
I’ve done this many times when “staging” sites, and since you are hosting both domains as the same user, it’s really easy and convenient.
edit: This paragraph is not accurate - thanks to Raz2133 for pointing it out . Bear in mind, you will need to install WordPress yourself, rather than a “one-click”, as “one-click” installation requires a completely empty directory to work (and your new “dev.subdomain.tld” will have some stuff, like Maildir, logs, some hidden files, etc in it). This, however, is really easy (wordpress.org) and should not present any problems for you (I mean, after all, you are using your “own” CMS now!).
You will have to make a small “tweak or two” in your WordPress config file after the renaming to account for the url change. If you consider this to be a minor issue, you should like this approach as you have the advantage of being able to develop the sites completely in parallel