You must use quotes to include a space in arguments for a GitCentric SSH command.
In addition, Microsoft Windows requires that you nest single quotes within double-quotes. In the example below, double-quotes are provided for the Microsoft Windows shell, and single-quotes are nested within the double-quotes for the SSH command-line parser.
C:\source\TestProject>ssh -p 29418 mylogin@localhost gitcentric config-branch --branch refs/heads/master -p 1 -e 3 -s 2 -d "'xxxx yyyy'" --initialSync git TestProject