C:\Program Files\World of Warcraft\WTF\Account\<ACCOUNT NAME>

There's a file there called "macros-cache.txt". Feel free to edit it all day long.

Sample contents:

[code:1]MACRO 6 "ACCEPT" Spell_unused
/script AcceptGroup();
/script AcceptQuest();
/script AcceptTrade();
/script RetrieveCorpse();
/script RepopMe();
END
MACRO 8 "FIREBALL" Spell_Fire_FlameBolt
#showtooltip Fireball
/assist focus
/cast Fireball
END
MACRO 9 "FIREBLAST" Spell_Fire_Fireball
#showtooltip Fire Blast
/assist focus
/cast Fire Blast
END
MACRO 11 "FOLLOW" Spell_Nature_Invisibilty
/follow focus
END
MACRO 10 "FROSTBOLT" Spell_Frost_FrostBolt02
#showtooltip Frostbolt
/assist focus
/cast Frostbolt
END
MACRO 5 "INVITE" Spell_unused2
/invite Betavas
/invite Gammavas
/invite Betadot
/invite Gammadot
END
MACRO 7 "NOVA" Spell_Frost_FrostNova
/castsequence reset=24 Frost Nova,,
END
MACRO 1 "POLY" Ability_CheapShot
/focus
/run SetRaidTarget("focus", 1)
/run if UnitSex("target")==1 then g="female " else g="male " end;s="Sheeping a "..g..UnitLevel("target").." %T";c="Party";if GetNumRaidMembers()>0 then c="raid" end;SendChatMessage(s,c)
/cast Polymorph
END
MACRO 12 "SB" Spell_Shadow_ShadowBolt
#showtooltip Shadow Bolt
/cast [target=focustarget, harm, nodead] Shadow Bolt
END
MACRO 2 "SB/PA" Ability_Creature_Cursed_04
/cast Shadow Bolt
/petattack
END[/code:1]

To further clarify, the structure of these is fairly simple.

[code:1]MACRO 2 "SB/PA" Ability_Creature_Cursed_04
/cast Shadow Bolt
/petattack
END[/code:1]

"MACRO 2" obviously identifies which macro it is.

"SB/PA" is the name of the macro. I keep macros named in all Caps due to old coding habits.

The third part of the first line is the name of the icon to use. I don't know where you'd go to find a list of all these names but I'm sure such a list exists.

The next part contains the macro itself followed by a new line and the "END" obviously marks the end of the macro.

Pretty easy stuff, no?