Logback: How to change log level for specific message and logger?

Question

I'd like change log level from error to warn for one specific combination of message and logger.

I have tried to filter out these cases and log it again with the new (warn) level. Filtering out worked, however the new log did not appear in the console no matter in which part of the code the logger was instantiated and called.

class CustomFilter : Filter<ILoggingEvent>() {
    val logger: Logger = LoggerFactory.getLogger(SqlExceptionHelper::class.java)

    override fun decide(event: ILoggingEvent): FilterReply {
        val messageMatches = event.message.contains("my message part")
        val loggerMatches = event.loggerName == SqlExceptionHelper::class.java.name
        val levelMatches = event.level == Level.ERROR

        return if (messageMatches && loggerMatches && levelMatches) {
            FilterReply.DENY.also { logger.warn(event.message) }
        } else {
            FilterReply.NEUTRAL
        }
    }
}

I have tried also Turbofilter in a similar way as here. I was able to see the new log in this case, but all the aruments of decide except logger and level were null, so I didn't manage to filter the log to be replaced according to the message.

I'm using Logback 1.2.11