Somebody is planning to move the subversion repository I work on (8000+ commits).
Is there a way to use git-svn to replay the last, say, 20 commits from the old location once the migration is finished?
(not only my own commits, but also other team members)
Bonus question: How do I add multiple svn repositories to my git local copy?
I'm not sure that git svn is the right tool for that job. The documentation contains the statement when discussing the --commit-url option:
Commit to this SVN URL (the full path). This is intended to allow existing git svn repositories created with one transport method (e.g. svn:// or http:// for anonymous read) to be reused if a user is later given access to an alternate transport method (e.g. svn+ssh:// or https://) for commit.
Using this option for any other purpose (don't ask) is very strongly discouraged.
I'm not sure precisely what that warning applies to, but it may apply to the "bridge" situation you are describing. If you decide to proceed with git-svn, you may be wise to proceed with caution.