Yes, you can. Go to the folder 'properties' inside your project. There you can find a file called naviox-users.properties, with this content:
# In plain OpenXava the users are added here in the form user=password
# If you want full management of users, roles and modules stored in database,
# get XavaPro from here: http://www.openxava.org/xavapro
admin=admin
Edit it, and add all the users you want with the pair user=password, in this way:
# In plain OpenXava the users are added here in the form user=password
# If you want full management of users, roles and modules stored in database,
# get XavaPro from here: http://www.openxava.org/xavapro
admin=admin
john=sjr3ji
juan=mso2rl
dorotea=mosoko
You have to restart your application in order it has effect.
To learn more about security and user management with OpenXava look at: https://openxava.org/OpenXavaDoc/docs/security_en.html