RopeJoint Length

[LemonLake]

I'm working on a game that has a wrecking ball, linked between the crane and ball with a single RopeJoint. The joint works perfectly, not an issue, however I would like to change the length of the RopeJoint during runtime. I've looked on the wiki, the forums and google and it appears there is no function for this. Is this true, and is there another way around? I'm using Löve 0.8.