New system property bamboo.svn.wc.format has been added. It can be specified via command line (-Dbamboo.svn.wc.format) and take values: "1.3", "1.4", "1.5", "1.6"
This option will set format for all newly created Subversion workspaces. It does not affect existing workspaces.
Please also make a note that option bamboo.svn.compatibility.14 is deprecated in favor of bamboo.svn.wc.format