title: change attribute value in Core Data in already published application
body: <p><em>(Actually, I don't know how to formulate my question, so in google I found nothing.)</em></p>
  
  <p>So, the situation: In app in appstore I've the Core Data entity (let's say Weather), one of its attributes is Speed type String. Now it contains single line (e.g. 5 mps), but now I want it to contain an array-like string (e.g. 5 mps; 6.4 mps; ...) also change name from "Speed" to "SpeedHistory".</p>
  
  <p>And I made a new model verison, chose it (it has little checkbox now), renamed the attribute, set "Renaming ID":"Speed" and now: how should I act, to prevent user's of old version data crash?</p>
  
  <p>Could you give me some advice, please?</p>
  
  <p>P.S. Data in Weather Entity is fulfilled by user. And I'm using MagicalRecord.</p>