CheckProperty and the text in the log

There is an OnLogCheckpoint event handler available in TestComplete.  Basically, when you log the checkpoint, it fires that event.  You can then assign code to the event to execute each time the event fires.  Within that code, you can intercept the text of the message and change it before writing it out to the log.

https://support.smartbear.com/testcomplete/docs/testing-with/advanced/handling-events/creating-handlers/for-testcomplete-events.html

Because it's an event intercepting the writing of a record to the log, it only has available to it whatever is in the process of writing that log record.  String processing is your best bet.