I have been using Cogwheel's MacroSequence mod for offline macro editing.
Macro Sequencing Mod - Amazing for multiboxing

You edit the macros offline in a lua file, which is shared between all of your chars if they use the same AddOnns directory. To load changes onto a WoW client you just have to do a "/console reloadui". Each client just needs a short macro that calls the Cogwheel sequence via a "/click" command. For example:

Sequences.lua:
Code:
EarthShock = { [[
/stopcasting
/click [dead][noexists][noharm] BongosActionButton61
/cast Earth Shock
]] },

FlameShock = { [[
/stopcasting
/click [dead][noexists][noharm] BongosActionButton61
/cast Flame Shock
]] },
macros-cache.txt:
Code:
MACRO 7 "SyncSh" INV_Misc_QuestionMark
#show [modifier:ctrl] Frost Shock; Flame Shock
/click [modifier:ctrl] FrostShock; FlameShock
END
(BongosActionButton61 points to my assist macro. I use action bar page swapping to change which assist macro the button calls and therefore which char is my main.)
Using action bar pages to free focus.

Good points about this system:
  • I hardly ever need to edit the in-game macros. The part that I tweak a lot is in the lua file that I edit offline in my prefered text editor.
  • Keeps all of the macros in a single file, which helps me get my head around what my various toons are doing.
  • MacroSequence lets you sequence any slash command, so you can do some stuff that would be impossible with just in-game macros. For example, I have a "sequenced shock" macro that will sequence Earth Shock / Frost Shock between my 4 shamans, interrupting casting on *just* the one that is due up to shock.