It is possible to test a new email signature for one person, several persons or a group of persons without affecting existing users. This is done by applying filters on the email signature that needs to be tested.
Filters are based on email address, department or Active Directory user groups
Below an example of a the email being filtered to only be active for one users based on email address
In this example the email signature is for all users of a given AD user group
For more info on how to setup and manage filters click here