Yeah, that is possible, yoeu just need to write you own Format for big decimals that write in string and read the string to BigDecimals after that in all conversions you ned to explicitly use your own BigDecimals format.
Unfortunately, I have no control over data nor the data is the same format every time (its ElasticSearch web admin). So in Elastic json is stored as long and I cannot change it as it will be a very huge and bad for performance task. Is there a way to dig in standard parser/stringifier?
If you cant control the format of the ElasticSearch maybe you can change the data type that has been pass to it. Someone need to give the data to ElasticSearch can you change the type of these fields to save as string instead and transforms these fields into BigDecimals at the end of the process ?