:%s/^\(from.*\)\(import.*[a-z]\)\%>79v/\1\\\r\t\2/g
... to change long lines like ...
from experimental.tools.musicexpressiontools.RhythmRegionExpression import RhythmRegionExpression
... to two shorter lines like this ...
from experimental.tools.musicexpressiontools.RhythmRegionExpression \
import RhythmRegionExpression
... in a single command.
