switching to a Designer template), then there is likely be to a time-period when your blog looks strange: some of the changes will be done, some won't, and maybe some key features won't look right.
Many people look for a way to re-direct their blog or to display a temporary vacation-notice ("closed for maintenance, come back soon") while they make the changes.
However the only option that Blogger has is making the entire blog private (Settings > Permissions > Blog-authors-only). This isn't really suitable, though, because it just shows prospective readers a standard message saying that the blog cannot be accessed, without explaining why. It may even harm your blog's reputation, if someone influential happens to look at it just at the wrong moment.
Since there is no other work around (except for blogs with a custom-domain - see the last section of this post), Blogger administrators have to plan their changes carefully, and put them in place quickly.
Plan carefully, and make the changes quickly
If you blog has a .blogspot URL, or if you don't like the alternative suggested below, then the only option is to plan your changes very thoroughly so you can minimise the time that your blog is in transition.
The first step in planning is to make a private testing blog that's like the real blog (except perhaps it only has 2-3 dummy posts instead of your real conent).
Work out exactly what changes you need to make, and the exactly details of how to make them. Use the test blog, not your real one, to do all your research, experiments etc.
Keep a listSo you know exactly what changes need to be made.
When I did this recently, I used Excel because I'd used it to find the difference between two template files. But there are many other suitable tools, ranging from the back of an envelope on your desk to a draft post in your blog, or even a full-blown change management system.
PrioritizeSort the list so that the changes that must happen first are at the top,and the things that aren't so important are at the bottom.
What's important to you may be different from what's important to your readers: when I did changes to my local site, re-installing Google Analytics was the first thing to do after changing the template, because collecting statistics is very important to ME. But if I'd been totally reader-focussed, I'd have done things last, and done all the things that readers see first.
Combine things:Consider whether some items on the list can be done at almost the same time
Eg if you need to customise the template for several items on the list (eg center the heading, hide the navBar), and all the customisation can be done by entering new CSS rules then these can all be done at the same time.
(These two steps may give conflicting results: but if you prioritise first you'll be able to make good decisions about what's most important.)
Choose a time of dayChoose the best time to make the changes. This could be when your blog has a relatively low number of visitors, or you may use some other criteria.
For a blog that's used by people in my city, I chose 12-midnight when very few people are interested in the topic. But for Blogger-hints-and-tips I chose 9am (local-time for me is Western European time) because most readers are 4-8 hours behind my time zone.
Warn your readersSome people recommend making a temporary post telling readers that you're making changes and apologising for things looking strange. There are cases when this would be a good idea, but overall I'm not convinced: most of your readers probably won't visit while you're making the changes - except that a post like this going out on your RSS feed might just encourage them to visit now to see the new look. And readers who get to your blog via search and go straight to an older post may not see the post anyway.
Do the changes, quicklyWork fast, but be careful and methodical too: work through your list, and tick off items as you go. If you have an brilliant ideas about what else you could do, resist them at least until you've got your core blog features working correctly with the new look.
An alternative for custom-domain blogs
If your blog is published to a custom domain, you could:
- Prepare a temporary "come back tomorrow" message using another tool (eg Google Sites - or even just another blog with only one post)
- Switch your main blog back to published on Blog*Spot
(Setting > Publishing > Switch to Blog*spot)
- Re-direct your temporary message (site/blog etc) to use the custom domain
- Do the changes to your blog
- Undo the redirect for your temporary message
- Re-publish your blog to the custom domai
Of course this won't work for people who navigate directly to one of your posts instead of going to the blog and itself (eg to http://blogger-hints-and-tips.blogspot.com/2010/07/coverting-ms-word-documents-to-blogger.html instead of http://blogger-hints-and-tips.blogspot.com/) - if you get a lot of visitors from Search, then they probably enter your blog this way.
Also, if things go wrong during the re-direct processes it could take a bit longer than you planned to resolve the registry entry problems. (Things don't usually go wrong, but it may not be worth the risk.)
Switching your blog to use a new Designer template
Making a private blog for testing template changes
Comparing two template files, using Excel