Hi Romain,
just tried this. Good news first: We have implemented redirections for legacy repository URLs.
Mercurial is following these redirects (at least version 4.8.2 at my machine), so here nothing has to be changed.
SVN only mentions the redirect, which then can be applied
▶ svn update
Updating '.':
svn: E170011: Repository moved temporarily to 'http://localhost:8080/scm/repo/svn/my-repo'
▶ svn relocate http://localhost:8080/scm/repo/svn/my-repo
▶ svn update
Updating '.':
A some_more_file
Updated to revision 2.
For git you can configure the client to follow redirects:
git config --global --add http.https://my.server.com.followRedirects true
Hope this helps.
René