Copy pasted from here! "You are free to create as many accounts as you like and you are welcome to trade between your accounts just as you would with any other legitimate player."My goals and achievements on F2P accounts! ---> Thread! <---
Check the rules, you can create and use multiple accounts but not to break game mechanics, such as rig mini-game results. This is quite vague and allows Jagex to have discretion about what actually is an abuse of game mechanics.
But in short, if its not damaging others gameplay, and isn't breaking other rules it should be fine.