Can you set custom ID's to flex objects?

Hello, I'm trying to make my own flex-object type. I read in the documentation
that:

By default, flex-objects page type takes two URL parameters, directory and id. They are used to navigate directories.

The example shown on that page suggests that the ID is randomly generated. I'm wondering if I can set my own unique ID's per flex-object? Like if I use one of the flex-objects fields that expect a unique value.