Use "route_category" in sth::emulation_bgp_route_config which is implemented in 4.50GA release of HLTAPI.
[route_category UNDEFINED | PRIMARY | SECONDARY | UNIQUE]
Possible supported route categories:
UNDEFINED : The default category assigned to a manually created block
PRIMARY : A preferred route that has duplicates (secondary routes) advertised by other ports
SECONDARY : A less preferred backup route
UNIQUE : Indicates that a single port in the test configuration advertises this route