I have two MySQL instances running with the same schema. One is in the cloud; one is on my local box. The local-box version needs a couple of test rows in its main table.<
If you're already familiar with mysqldump, I'll remind you that mysqldump has a --where option, so you can get a single row if you write the condition for that:
mysqldump databasename tablename --where "id=12345" --no-create-info --skip-add-locks --host=db1 | \
mysql --host=db2
You could also use SELECT...INTO OUTFILE to dump the result of any query you want into a flat file, even a query of a single row. Then LOAD DATA INFILE to import that file on the other instance.
You could also write a simple script in your choice of language. Connect to both instances. SELECT a single row from the source instance, save it in a variable in the script. Then form an INSERT command to execute against the destination instance. This may not be the most efficient way to move a large amount of data, but for a single row it would be fine.