Yes, of course! The easiest way to add a single subscriber is by going to Subscribers -> Add subscribers -> Copy/Paste subscriber list and type in all the needed information for that subscriber and separate each information unit with a comma.
If you need to add two or more, simply enter each subscriber’s information into a new row.
After you click Submit, allocate each piece of information to a corresponding custom field and make sure to choose at least one group to import the subscriber to.
After that, simply click “Start import” and wait till the subscriber appears in your list.