I would like to share a script to add tables in existing publication in transactional replication,

USE PublisherDB
GO
exec sp_addarticle 
@publication = N'PublicationName', 
@article = N'TableName', 
@source_owner = N'SchemaName', 
@source_object = N'TableName', 
@type = N'logbased', 
@description = N'', 
@creation_script = N'', 
@pre_creation_cmd = N'drop', 
@schema_option = 0x00000000080350DF, 
@identityrangemanagementoption = N'manual', 
@destination_table = N'TableName', 
@destination_owner = N'SchemaName', 
@status = 24, 
@vertical_partition = N'false', 
@ins_cmd = N'CALL [sp_MSins_SchemaNameTableName]', 
@del_cmd = N'CALL [sp_MSdel_SchemaNameTableName]', 
@upd_cmd = N'SCALL [sp_MSupd_SchemaNameTableName]',
@force_invalidate_snapshot = 1
GO

You can read the earlier post to get details of publications, subscribers and articles at http://beyondrelational.com/justlearned/posts/688/find-the-details-of-publications-subscribers-and-articles-at-once-in-replication-sql-server.aspx