This is a short how-to in the topic of changing a wordpress.com blog owner username. We are going to do a trick, which worked for me well, but be careful, do not blame me for any kind of accidental blogname loss.
So, there is a way to do a wp.com -> wp.com blog transfer with same domain, when you have the new username added as administrator in the original blog.
If you miss up something, you won’t be able to recover your blog or it’s name, so read first. (Maybe export your blog and try the how-to on an empty blog also, before you start)
-if you need the e-mail address of the original user name, then change it to something else and verify it in the e-mail sent to the new address. (log off – log on – check it.)
-make a second user name (https://en.wordpress.com/signup/?user=1) this time choose one, which you like, but do not make a blog.)
-add this second user as administrator to your original blog (users/add user)
-transfer your blog to the new user profile (dashboard/my blogs)
-verify this in the email sent to the original user’s address. (click on the link)
you can loose your blogname here, so be careful: if the wp.com asks for a new blogname, then you have done something wrong, just do not continue. (check if the new user is really added as administrator and start again the transfer)
-if everything is ok, the blog will be transfered, without asking for a new name.
-there you are, thats all, next time be smarter (than me – also)..
-the original owner is now removed from the blog (as owner and as admin also), but it’s user account cannot be deleted because of wp.com policy.