This smells like an XY Problem.
If all you really want is to be able to see specific log entries see How to watch and look through logging. There are all sorts of ways to watch and extract logging for specific Items without changing anything about how it logged in the first place.
As Matthias suggests, maybe persistence and charting is a better approach to see what you are after.
If you really need these in a separate file for some reason, you could configure log4j2 to log out some Item events to another file but it will require modifying the existing config for events.log to no write out those Items and a completely separate logger config to only write out those Items. You’ll have to get good at log4j2 config and regular expressions since you’ll need a filter to identify those entries to long and not log. events.log logs out the events on the event bus itself, it doesn’t have a separate logger for each and every Item. See openHAB - Filtering event logs (note these need to be translated to XML on OH 3).