[s]Actually after monkeying with this for days and thinking about some of the stuff written above I think I found a solution that makes this whole thing work... [/s]

Edit:
Well I thought the one below was working, however while it does prevent the retargetting problem of a character trying to assist itself, it doesn't allow for focus sheeping as the mage will attempt to fireball its hostile focus..... Argggg... more work ahead.

#showtooltip Fireball
/a [target=focus,help]focus;[target=focus,exists] party1
/stopcasting [mod:alt]
/use [mod:alt] 14
/use [mod:alt[ 13
/cast [mod:alt,harm] [target=targettarget,harm,mod:alt]Fire Blast; [harm][target=targettarget,harm]Fireball

To paint the picture my typical party = tanking pally Maivis, Mages Neeva Nynia and Tyia and Holy Priest Mirdyn. Other macros are in place to change their focus to specific characters when activated (as listed below).

Now the fireball macro does some very specific stuff based on criteria below
  • if focus exists and is helpful, assist focus and cast fireball,
  • if focus exists and is not helpful (harm or neutral) assist party1 and cast fireball
  • if no focus exists cast fireball on current target without trying to assist anyone...
  • if alt is pressed do the above but cast fireblast instead of fireball and activate trinkets.

Focus pass to a different party member by name used by all party members except Neeva

Focus Pass #3 (bound to ctrl+alt +3)
/focus [target=neeva,exists,nodead] Neeva
/Script ChangeActionBarPage(1);
/script SetView(3);
/stopmacro [nomounted]
/follow focus

However on Neeva that macro reads as follows, so with above fireball macro not trying to assist anyone if focus does not exist, she will fireball her current target with impunity and the rest of the party follows her cast...

/clearfocus
/script ChangeActionBarPage(2);
/c ky Set and in Charge
/script SetView(3);
/stopmacro [nomounted]
/follow focus

What was happening previously was Neeva was setting her focus to herself, so Neeva's focus = Neeva. When trying to cast a fireball after changing targets quickly, the macro would attempt to assist itself and pick the old target resulting in having to wait a second after changing targets in order to cast fireball on the intended target (generally meaning a quick death in pvp). So after retooling a bit all my mage macros work fine after passing focus quickly

Note because of the inclusion of [harm][target=targettarget,harm] the mage could assist a healer in the process of healing someone and still fireball the target of whomever the healer is healing...