In order to copy a Tagged Value named "mytag" from the source model to the target model you can add the following to the Class template (Ctrl+Alt+H):
%if classTag:"mytag" != ""%
Tag
{
name=%qt%mytag%qt%
value=%qt%%classTag:"mytag"%%qt%
}
%endIf%
For more information on transformation templates see:
http://www.sparxsystems.com/enterprise_architect_user_guide/8.0/software_development/transformationtemplates.html