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You have to learn a bit and stop being a noob, but when you start, you'll find it's easier than you think. Just expect to spend a while until everything starts to make sense.

Download the .scad file, download OpenScad and install it, then open the .scad file.

Near the top, there are several sections in which you can change the values and play with : / [Box dimensions] / down to / [STL element to export] /

BTW, I'm planning on doing the same thing - my current project is made up of 3 boards. If you really don't want to spend the time, I may post my mod on the site, maybe as a remix.

Now this part won't make sense to you at the moment, ignore it for now because until you have learned more, it will just confuse and frustrate you, and might make you give up. Come back to it when you understand Openscad a little better.
The PCB feet are done in a section called "module Feet()". Right at the very end is a section that starts with if (PCBFeet==1)
These two sections can be duplicated to make two PCB feet. You don't have to stop and 2 boards, you can have as many as you like.

If you do this successfully, please upload it for others to use, and when you do, please ensure you give Heartman credit for his hard work. Of course, don't hesitate to credit yourself for YOUR hard work as well.

Good luck.