You would first play with an entry and see which value is assigned to "Rich Text" and which one to "Convert Line Breaks".

Then you would write an SQL command which to update the 'entry_convert_breaks' column from inside the 'mt_entry' table where the 'entry_convert_breaks' is set to something, and the blog id is something, the 'entry_convert_breaks' column' will be something else...

I was under the impression that selecting "Convert Line Breaks" performed a browser/client-side conversion to convert line breaks into

tags. The change only takes place in the browser until you press the Update button.

If that is the case, then a database edit would require retrieving the entry content from the database, using a regex to parse the text, and then updating the database.

If it turns out I just have to change one column (and publish), that sounds much simpler. I can try updating it for 1-2 entries, publishing and seeing what happens.

I'm an experienced developer, so just trust my judgement and you would solve the problem in an effective manner ;)

mysql> select entry_id, entry_basename, entry_convert_breaks from mt_entry where entry_convert_breaks IS NOT NULL;
+----------+-----------------------------+----------------------+
| entry_id | entry_basename              | entry_convert_breaks |
+----------+-----------------------------+----------------------+
|      470 | allaboutjohn                | richtext             |
|      471 | site-history                | __default__          |
|      478 | material-things             | __default__          |
|      534 | lentils                     | __default__          |
|      538 | scattered                   | richtext             |
|      539 | floor-fan                   | __default__          |
|      548 | honeymoon-pictures          | 0                    |
|      550 | website_maintenance         | richtext             |
|      549 | basement-junk-and-treasures | __default__          |
+----------+-----------------------------+----------------------+
9 rows in set (0.00 sec)

mysql>  update mt_entry set entry_convert_breaks = "__default__" where entry_convert_breaks IS NOT NULL;