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
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