It would be nice to have activity that would update a particular column on all rows of a list:
Update allow rows of <list>.
The second step would then make it conditional: Update allow rows of <list> if <column> <condition> <value>
Maybe, the code would like something like this.
SPSite Site = (SPSite)__Context.Site;
SPWeb spWeb = (SPWeb)__Context.Web;
SPList List = spWeb.Listsnew Guid(this.ListID);
int nCount = List.Items.Count;
for (int iCount = 0; iCount < nCount; iCount++)
item = List.ItemsiCount;
itemColumnName = NewValue;