I don't understand your question.

What is your understanding of "identities"? What I mean is that I don't understand what you mean by "identities". In Thunderbird they are effectively aliases of a "real" email address.

Where are you exporting to and importing from?

In Account Settings, there is a button named Manage Identities. This feature is used to add new identities. My ISP allows multiple email addresses of the form, anything@username.plus.com. In Thunderbird, any of the identities can be used as "anything". All this can be in one Thunderbird account, and it provides the option to use different email addresses for different contacts or groups of contacts. I have a list of identities in Thunderbird on my old laptop, I want to transfer them to my new one. I hope this helps.

I don't know of any way of exporting or importing account settings. I'd view the identities feature as simply a subset of the accounts. And the way to move accounts between instances of Thunderbird is to copy the profile form one to another.

The usual advice given about moving Thunderbird-related data between computers is to copy the entire profile, so the new installation looks identical to the previous. Alas, by the time most users come to a forum seeking help, they have already done it the hard way, having set up their accounts from fresh. Once you've started using your new profile, you will have data in two places that can't easily be merged.