I am using the K2 tools archive and ive just noticed that it only outputs a list from the last twelve months. Is it possible to increase this to all items?

Hi , no unfortunately there is no option for that. You will have create your own module based on the K2 Tools and then modify the code.

OK, I make changes in code so can i write here for someone else?

I would recommend creating a new module instead of hacking core files.
You will not be able to update smoothly.

You can publish the module at getk2.org/extend/extensions or a simple github repo is good and it will help other users.