I am not aware of any way to "level" an existing CPG. New LDs will be created on the new spindles, but all existing data will just stay put on the original spindles. Using DO is a workaround to force the data off the old LDs onto new LDs, and to do that you have to move it to a new CPG.
Note that the new CPG can have exactly the same settings as the old one. You don't need to change RAID levels or anything, just as long as it maps to all spindles if the same tier (which is the default AFAIK).
You do want to run compact on the old CPG as you move stuff off to get it to release the old LDs, so that you can reuse those chunklets for your new LDs. Not doing this may end up with your new LDs biased towards the new spindles and may force your new LDs to be located mid-platter rather than the preferred "faster" tracks.
If you are coming from an EVA background some key things to remember:
- Unlike Disk Groups, a single physical disk can belong to more than one CPG.
- LUNs in a CPG are not actively levelled. New allocations tend to cause an overall levelling effect by biasing the new data on the new spindles. This results in old data on old spindles and new data on new spindles, and not all data on all spindles.