Whether extract/repliact can be dynamically changed ?

Hi,

1) I am trying to check whether " i can able to add new table/columns to the replication paramaters (extract/replicat) on the fly without restarting extract/replicat .

2) And in our environment we are replicating specific columns from source to target. we have an additional column called "UPDATE_DT" in the target which gets updated with current date whenever new data comes. This column is getting updated even when a non replicated column in the source is updated since logically the logminer get this change from the redo log. Is there any possiblity of avoiding the UPDATE_DT column not to update if non replicating columns gets updated in the source