A simple way is to change the grid origin: (Pcbnew / View / Grid Settings).
Because of it's open-source-ness, a lot of side projects have sprung up around KiCad. Pcbnew also has an internal scripting interface, and you can find some scripts around the 'net, most are on github, but some are on external sites only.
An overview of (some of) these scripts is on:
https://github.com/xesscorp/kicad-3rd-party-toolsA script that may be useful to you is:
https://github.com/Laksen/kicad-bga-toolsThis script seems to be quite old though, and therefore probably written for an older version of KiCad, so probably it will not run without modifications.
Just Curious:
Why do you use SnapEda libraries?
These sometimes have some compatibility problems with KiCad, while there are already a lot of BGA footprints in KiCad. There are also Footprint wizards in KiCad and you can make new footprints very easily in KiCad (if they fit the wizard format).
Currently there are 13 Footprint wizards in KiCad, and rectangular BGA's is one of them.
Scripts and Footprints Wizards are both written in Python, so if you want similar, but not quite, the behaviour of them, they are relatively easy to adjust.