Are people allowed to cut or bend parts? Are we allowed to cut parts to create official vex parts (Ex:cutting a 2in shaft to create a 3in shaft)?
Yes, you are allowed to freely cut and bend parts, provided you don’t violate any other rules in the VEX Skyrise Game Manual. Specifically pay attention to <R15> which details what type of modifications are illegal.
We’re assuming you made a typo and meant to type “cutting a 12in shaft to create a 3in shaft”. If our interpretation is correct, what you have described is a legal modification.