Change ILM policy


I have a cluster of 2 nodes HOT and 1 DATA warm,
and my ILM configuration is set to 1 shard and 1 replica

I checked today my indexes and I found out that My HOT data node is going to hit 90% of DISK, and after investgation I Think if I understand well it's because the one of replica or shar pass to the warm node, but the other can't go anywhere as I have just 1 DATA node.

I would like to know if this way of thinking is correcte, and in this case if I configure ILM like that by making in WARM phase 0 replica, if it will solve the problem, and if I will not have errors after editing it, as packetbeat is already sending data, or should I stop packetbeat before editing the ILM policy

Hope I explain well my problem
Thanks for your answers