Yes! We recommend you do this by setting up a separate Leanpub account for each pseudonym. To do this, enter your pen name or pseudonym when you create your account.
If you have already created an account, you can change your name to your pen name here: https://leanpub.com/user_dashboard/settings.
The name you enter for your account, and your profile image, will be displayed on your Leanpub web pages and in each of your publications.
For this reason, we recommend you set up a separate account for each pseudonym.
We do also have a kind of "secret feature" you can use to edit the author name on a per-book basis. To do this, go here:
(Please make sure to replace YOUR_BOOK with your book's actual address!)
There, you will see a link that says "Edit Your Author Information Shown On This Book Only"
However, there are places on Leanpub where this author information may be shown with your account profile image, and we've had a report that it can sometimes appear next to your actual account name. (It's an old feature made for a specific case.) Partly for that reason, we recommend you set up a separate Leanpub account for each pseudonym.