Adding a New Column to Table B: Preventing Overwriting in Data Mapping

I have 10 columns in a table A, I do "write to table" and map 4 of them to write to table B and execute that now i have 4 columns in table B. I now want to write one more column from table A into table B. If i edit the "write to table" column and add it, will it ONLY write that new column to table B, or rewrite the ones I already did previously?