Castsequence with multiple targets. Would this work?

I want to create a healing rotation macro for my shammy team, but when it's not their turn to heal (with the smart heal macro) I would like them to cast lightning bolt on the mains target. So i was wondering if this setup is possible and I could use some help working it out.

For toon 1
/castsequence reset=combat [help] [target=targettarget, help] chain heal, [target=focustarget,harm,nodead,exists] lightning bolt, [target=focustarget,harm,nodead,exists] lightning bolt

For toon 2
/castsequence reset=combat [target=focustarget,harm,nodead,exists] lightning bolt, [help] [target=targettarget, help] chain heal, [target=focustarget,harm,nodead,exists] lightning bolt

For toon 3
/castsequence reset=combat [target=focustarget,harm,nodead,exists] lightning bolt, [target=focustarget,harm,nodead,exists] lightning bolt, [help] [target=targettarget, help] chain heal

Any help would be appreciated

You can't change targets in a castsequence.