I'm not sure exactly what you're looking for without knowing more what you mean by multi-line editing, but you can apply arbitrary commands (including inserts) to any set of lines.

Switches case on lines 4, 15:

:4,15 norm ~

Indents text and changes the first two words of ever line to "duck" from mark a to the end of the file

:'a,$ norm >>2cwduck

Prepends a # to every line of the visual selection

:'<'> norm I#

Applies regex to lines that match a regex

:g/ducks/ s/moo/quack