If you can work in extractors to only get the values you want out of the message, that would work - perhaps an well built GROK statement…either in extractors OR in the pipeline
You could leave the extractors in place and then drop the extra fields in the pipeline with the aforementioned functions… or you could drop the extractors all together and separate out your fields in the pipeline where you would only create the fields you want… Someone created a pipeline rule to do just that here It’s not necessarily efficient… but it works…