The full combined macro is too long so you'll need an addon that increases the length limit for macros.
Code:
#showtooltip
/cast [pvptalent:4/1,@arena1,mod:shift,harm][pvptalent:4/1,@arena2,mod:ctrl,harm][pvptalent:4/1,@arena3,mod:alt,harm][pvptalent:4/1] Viper Sting; [pvptalent:4/2,@arena1,mod:shift,harm][pvptalent:4/2,@arena2,mod:ctrl,harm][pvptalent:4/2,@arena3,mod:alt,harm][pvptalent:4/2] Scorpid Sting; [pvptalent:4/3,@arena1,mod:shift,harm][pvptalent:4/3,@arena2,mod:ctrl,harm][pvptalent:4/3,@arena3,mod:alt,harm][pvptalent:4/3] Spider Sting
Or if you don't use a focus target for anything else you could use this one
Code:
#showtooltip
/focus [mod:shift,@arena1,harm][mod:ctrl,@arena2,harm][mod:alt,@arena3,harm][]
/cast [pvptalent:4/1,@focus] Viper Sting; [pvptalent:4/2,@focus] Scorpid Sting; [pvptalent:4/3,@focus] Spider Sting
/clearfocus
Or if you don't mind briefly changing targets you could use this one
Code:
#showtooltip
/target [mod:shift,@arena1,harm][mod:ctrl,@arena2,harm][mod:alt,@arena3,harm][]
/cast [pvptalent:4/1] Viper Sting; [pvptalent:4/2] Scorpid Sting; [pvptalent:4/3] Spider Sting
/targetlasttarget