Is this a scam?

No, this is no scam. It has been tested and verified by several different runescape cheatting websites.

How can you do this?

I have found a way to send different java codes back to the main server which temporarily overides their system and changes the code of your level from whatever it may be to whatever I want.

Is this known of?

No, this is entirely new and Jagex does not know about this yet. So you better hurry up before they patch this.

What do you use to do this?

I use my own special made client interface I made myself. It has the option of sending the different java codes to the server and has some other handy runescape tools. Below is a screen capture of what my client looks like.