Swapping the control rod for numerous smaller heatsinks, while adding an energy converter to power the gravity launcher. A brilliant feat of Engineering Indeed...
*phone rings*
...What? Oh, Killy? Sanakan wants her launcher back?
Watching images like this makes me imagine some badass story where mankind is facing doom due to an alien invasion or something, with the denizens of Gensokyo deciding the save them. Sharing their divine weapons, human scientists are allowed to examine Okuu's cannon and the technology in it. They then use their newfound knowledge to pimp her up 1000%.
...perhaps someone could make a comic of it one day.
You know how it initially appear from a thumbnail, where it looks like a lot of cannons... kind of reminds me of Cloud Strife's Omnislash ver. 5 from Advent Children.