August 2016 Update: Change the base branch of the Pull request finally allows you to change this branch.
(And that closes question 18 , which was 3 years old and had 1,500+ comments)
After you create the transfer request, you can change the base branch so that the changes in the transfer request are compared with another branch.

Original answer:
Since PR cannot be edited in terms of a branch (see below), the simplest way would be:
- create a local new branch on top of the current branch
- click this new branch
- create a new PR with the desired destination.
- close previous PR
- refers to the "old" pull request from the new; eg.
Supersedes #123 (as described below by Rivera )
(original answer, valid only when creating PR)
You can try and select a different base branch , as in the section Changing the range of branches and the recipient repository "(By clicking the Edit button at the top of the PR page)

The easiest way to think about a range of branches is as follows:
- base branch - this is where you think the changes should apply,
- the branch of the head is what you would like to apply.
Change changes to the underlying repository that is notified of the migration request.
Anyone who can click on the base repository will receive an email notification and will see a new transfer request in their panel the next time they log in.
If you select the base branch of the one that the original maintainer (owner) wants to use, your PR should merge from your branch (unchanged) into a new base branch.
VonC Jun 11 '14 at 9:21 2014-06-11 09:21
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