How can we add a column without having to reinitialize the entire publication. What is the procedure to do it?

Simple go to the replication properties and click on the 'Filter Columns' tab. at the bottom u would get a button named 'Add Column to table' when u click u r asked for the column name and the type also add NULL at the end because u cannot add a column with a not null constraint.

RegarDs,

JacX