Create field based on an existing field in Elasticsearch - elasticsearch

Question

I have an Elasticsearch index that stores products and it's properties like size, color, material as a dynamic field:
"raw_properties" : {
"dynamic" : "true",
"properties" : {
"Color" : {
"type" : "text",
"fields" : {
"keyword" : { "type" : "keyword", "ignore_above" : 256 }
}
},
"Size" : {
"type" : "text",
"fields" : {
"keyword" : { "type" : "keyword", "ignore_above" : 256
}
}
}
}
}
An indexed document looks like this:
{
"_index" : "development-products",
"_type" : "_doc",
"_id" : "3",
"_score" : 1.0,
"_source" : {
"raw_properties" : {
"Size" : ["XS", "S", "XL"],
"Color" : ["blue", "orange"]
}
}
}
The problem is, that the value of raw_properties comes from various sources, and they differ a lot. For example, the field Color is called Colour from another source, and blue could be light-blue and so on.
So, I've implemented a normalization step in my app, that does a simple mapping like this (for simplicity, the mapping here is just a Ruby Hash, in reality the mapping is read from a database):
PROPERTY_MAPPING = {
"Colour_blue" => ["Color", "blue"],
"Color_light-blue" => ["Color", "blue"],
"Size_46" => ["Size", "S"]
}
When my app indexes a product, it looks into this property mapping and normalizes the property. This keeps the cardinality of the fields low and the user isn't presented with too much properties to filter.
The problem: Updating those mappings is pretty slow, as I have to reindex the affected products by applying the new mapping in my app and sending the data to Elasticsearch. I'm dealing with about 3 million products here, and new data with a new normalization comes in every day. I try to only find the products that are affected and so on, but it is still too slow.
So I was thinking if there was a way to do the normalization inside Elasticsearch? I've read about enriching data (https://www.elastic.co/guide/en/elasticsearch/reference/master/ingest-enriching-data.html) or the pipelines with processors (https://www.elastic.co/guide/en/elasticsearch/reference/master/ingest-processors.html) and had a look into Painless.
The main idea would be to only update the mapping, do an update_by_query, and let Elasticsearch take care of the rest.
So, I'm not sure if this is possible at all or where I should start. Any advice or hint is appreciated!