Impact of adding multi-field to existing field with PUT mapping API in PROD

Hi,

We are using Elasticsearch 6.2.4 in production.

Due to a new requirement, we need to add a new multi-field to an existing date field. We are using PUT mapping API for the same.

PUT {index name}/_mapping/{type name}
{
"properties": {
"indexedTimeStamp": {
"type": "date",
"store": true,
"doc_values": false,
"format": "epoch_second",
"fields": {
"dv": {
"type": "date",
"format": "epoch_second"
} } } } }

Is it safe to do this in PROD with large (upto ~100GB) shards?

What are the expected effects of this command? Increase in IOPS / CPU? Would we see throttling?

Thanks!

It will just update the mapping.
If you don't reindex, no change will happen on the existing data.