There are two types of components (ISMs) in ASMM: Business Logic (BL)-based and non BL-based.
Log level and log message are predifined in non BL-based ISMs. You can only filter log messages based on log level either in UI or in gatherer.ini file.
In BL-based ISM you can add your own log messages and define its log level. Also you can use some flag inside ISM that will either enable or disable log message. Be aware that log messages can affect performance of the system in a bad way.