String transformations in modify_fields

[gauee]

I am looking for an option to modify the record by appending, subtracting or replacing operations.

Case 1: When parsing input data like {"message": "First line#012Second line"} the value can’t be modified to {"message": "First line\nSecond line"} to allow multiline display in LogExplorer.
Case 2: When parsing input data like {"message":"hello world!"} the value can’t be modified to {"message":"yay, hello world!"}

Similar capabilities are achievable with fluentd record_transformer filter.
Existing logging-processor-modify-fields allows to replace value only if their are equal.

[quentinmit]

Today we only support full string replacements, as you found. What interface would you like to see for more complicated string transformations?