Are there any guidelines to follow if i want to drop a column in a custom table; or do we modify the xml and then propogate changes to the database and that is enough? What is the best way, or is there a best way?
I do not see anything on the campaign documentation on dropping columns.
If your schema leads the underlying SQL structure, yes, you can delete the element/attribute corresponding to the column in the schema, then propagate the change with Tools/Advanced/Update database structure: Updating the database structure
But if you do the invert thing, that means, if the mapping is SQL-directed, you delete the column in the database engine, then you must use the other advanced tool Extend database to apply the change in your schema, or most often, do it manually (often easier if change is quite simple).
Please take care, because there could be indexes, or relationships based on the column to be deleted. And of course, data to be saved through a table backup is often a good recommendation.