Yes. You can change your screen name as much as you like. This might be a bit confusing for friends or family who use Flickr too, but go for it!
Someone's written a testimonial about me. What if I don't want to publish it?
That's totally up to you. When someone writes a testimonial about you, there will be a little flag on your home page that takes you to a page where you can either publish or delete this new testimonial.
You can go back to this page any time, to see a summary of any testimonials you've written for people (both published, and waiting for approval), as well as any testimonials other people have written about you.
Can I point my friends towards a page that's mine in Flickr?
Yes! You can make your very own Flickr web address. You just need to choose an alias which will represent your Flickr page. Once you've set your alias, this cannot be changed, so think carefully!
Then you will have two addresses which you can share with your friends, that will look a bit like these: