How to deal with settings when extending existing nodes



I have the following situation:
I developed a node, and it was used by a user. After that I added additional settings (for example SettingsModelBoolean) and submitted this node to the user. User opens a workflow with this updated node and gets an error because that was no configuration for this new option.

In this case I have to catch this exception and use the default value.

But should I inform a user about it somehow? For example I can log a message about it.

Or I can mark this node somehow, and make a workflow as changed. 

I found a method setDirtyAfterLoad that is called if settings were loaded with warnings, but how to call explicitly?

What is the best strategy to extend existing nodes and keep the consistency with the previously saved settings?

Best regards,