Make a branch:
NOTE THE REVISION NUMBER (basenum) AND LEAVE A USEFUL LOG COMMENT. OK, now make edits commit them etc on the branch. At some point you want to merge the changes in to trunk (run this while in the trunk directory):
svn copy trunk ./branches/nw3
Where basenum is the revision number at which the branch was made and currentrev is the current revision.
svn merge -r basenum:currentrev https://swiftng.svn.sourceforge.net/svnroot/swiftng/trunk