The Identifier is only used to differentiate between multiple plugins, if you are using multiple plugins at the same time. If you have just a single plugin, it doesn't matter what the value is. It is also not used to identify any other script in your project.
If you can share more information about what you are trying to do, I can provide further assistance.
I am developing a custom plugin for Wikitude. In the samples, upon attaching plugin script, I see a field named "identifier", which, according to the documentation should be unique. For e.g. in Plugins - Advanced scene (attached image), it is set to Custom Camera.
I was wandering where it is set in a custom script? So if I have a script having a name, "MyCustomCamera.cs" in some other folder, what shall I enter in the identifier field? Adding "My Custom Camera" is not picking this script.