This mod is very easy because i have already modded all the files for you.

for this, you will have to be jailbroken and have iFile.

what you will have to do is download this file on your iDevice:
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go to this directory in iFile /Var/mobile/Library/Downloads

unarchive the rar file then copy all of the .bundle files

go to the directory /Var/mobile/Applications
and find the kitten cannon application, mine starts with F0530416. click on it, then click on KittenCannon.app and paste the files there. replace the old files and your good to go.

The modded files will get you to the highest possible score, but they will take around 20 minutes per level.
to get the highest score, the cannon has to be at 33 degrees and at 100% full strength. you will be in the top 5 on the leaderboards, right behind me