reset parameter can be a number of things, change of target, timer, key modifier, etc.
Basically for the castsequence command:
/castsequence [reset=n] skills, items, etc.
where n can be target, which means if you change targets your next use of the macro will be the first cast listed, so for a Warlock who has this:
/castsequence reset=target Curse of Agony, Corruption, Immolation, Shadow Bolt
note: there are no brackets around the reset parameter
Will cast CoA first then Corruption, and if he/she changes targets after this then the next spell cast will be CoA and not Immolation.
So for your purposes of pickpocket:
/castsequence reset=target Pickpocket, Cheap Shot
This macro would mean that you cast pickpocket on your first use of the macro and then cheap shot on the next, if you keep changing targets you keep on pickpocketing.
Oh and /castsequence does not account for resists/misses/parries/dodges, so if your spell/talent/cast is resisted it still moves on to the next one in the list.
Just some friendly warning, unless Blizzard stealth patched this, Pickpocket can be resisted, even on sapped targets, so I would use this macro with careful consideration when doing instances.