Avoid “big bang” rebrands – they are high risk (as these examples illustrate). It’s better to do things incrementally – that way you can validate that you’re on the right track. Lean Startup offers a wealth of suggestions on how to do this but here’s one more…
Imagine you want to rebrand Old Corp as New Corp. Why not run a randomised trial: show 10% of your users “Old Corp powered by New Corp”. Ideally you would show another 10% of users an alternative such as “Old Corp powered by Xyz Corp”. You can then compare metrics for the three groups (number of shares, pages per visit, time on site, frequency of return visits, etc) and see which performs best.
You can introduce New Corp subtly at first and then get bolder as you gather more evidence to support the switch. You could start really small… a single post “sponsored by New Corp”.
Welcome to agile rebranding.
BUT, don’t forget…
Before all this you might want to start with focus groups. And you should buy any assets such as domain names before going public!