Looking at the database schema, it seems that alert condition types that utilize a String condition would be limited to 256 characters.  What is your use case?  A really long pattern or something like that?

I've wrote plugin to monitor some connectors and I use condition field to pass error message. There are times where msg have 400 characters or even more...

Sorry, I don't fully understand.  What type of alert condition would you like to define as part of your alert definition?

I'm using "Trait Change". So alert contains 'Condition' field,  which is equal changed trait value.