Previewing another template online? Always when I want to check another template on my online site I have to download it to a local server, fix the blocks in that template, and set it as default. Only by that I could check it without changing the looks of the site online.

Let's say I want to preview this template online, without a local copy of the site, but also without switching the default template. Is this possible?

My final aim is to fix all the blocks in my new theme, and then preview it without setting it as default (So if visitors come in the same time they will see the site with the "old" template). 

Thanks,
Yes, you can install the ThemeKey module. One of its features is to provide:


  content, user, or role -specific themes


So you can upload a new theme and try it out for certain users roles, without affecting what how the site looks for regular users.