User screen name related settings

Here are some of the properties which can be override in portal-ext.properties file as per your requirement :

# Set this to true when you want the validation to allow for creation of
# numeric screen names.
  users.screen.name.allow.numeric=true

# # Set this to true to always autogenerate user screen names even if the user
# gives a specific user screen name. If this is set to true, the LDAP
# importer will fetch users by their email address even if the property
# "company.security.auth.type" is set to screenName.
users.screen.name.always.autogenerate=true

 # # Input a class name that implements
 # com.liferay.portal.security.auth.ScreenNameGenerator. This class will be
# called to generate user screen names.
 users.screen.name.generator=com.liferay.portal.security.auth.DefaultScreenNameGenerator

# # Input a class name that implements
# com.liferay.portal.security.auth.ScreenNameValidator. This class will be
# called to validate user screen names.
users.screen.name.validator=com.liferay.portal.security.auth.DefaultScreenNameValidator #users.screen.name.validator=com.liferay.portal.security.auth.LiberalScreenNameValidator