I have a highly ranked website... mysite.co.uk that I would like to rename mysite.com (the .co.uk is highly ranked because lots of sites link to it)
The question is, how do I rename/redirect without jeopardising the PageRank?
At the moment, mysite.com is pointing to the mysite.co.uk...
But... will Google allow this? And if so what will happen to my PageRank?
The official google guidelines for moving domains is to use a 301 redirect. It can take upto 3 months for Google to resolve a 301, but all the PR will be credited to the new domain. Many here have also complained about the difficulties Google has with 301's but I've always found them to work. It just takes a bit of time.
If I had a site that was highly ranked and had a lot of people linking to it.... I would leave it be! Why change a good thing - right? I would do what you're doing and just redirect the new ".com" to point to your ".co.uk".
Now, if you're talking about your company logo also being the name of the domain...still...leave your domains alone. Just change your logo on the site...nothing wrong with a company owning more than one domain.
If you're getting good results...I say keep it the way it is and just point the .com to your old site. Is there a particular reason you want people going to the ".com" domain instead of your ".co.uk" domain?
Did a renaming form domain1.com to domain2.com with about 30000 pages. Took around 4 months before domain2.com reached the same pagerank as domain1.com. Still ahve some problems with pages being spidered under domain1.com as duplicates even though they're 301ed.
It's a long operation, but the sooner you do it (if you HAVE to do it) the better.