What is the impact change exist rack id to another one

Hi, 

I have one question about the impact of change exist rack id.

we have a CDH 5 cluster with 6 data nodes(replication factor is 3), they are belong one rack rack0.

and we add 1 data node to this cluster, but it is added rack rack1 by mistake. 

now we met issue "Under-Replicated Blocks" due to only 1 node in rack1, it is need replicate 1 of 3 to node in rack1. but the disk capacity is not enough to storage 1 replica of all files.

Now, we have decomissioned the node in rack1, and want to change the node back to rack0.

my question is what is the steps to change the node back to rack0 safely? any suggestions?

Thanks!