Hello Kevin!
You can use expressions in Mass Product Changer.
Please use SQL syntax to replace test of description
example : =REPLACE([x],'test','ololol')
see screenshot -
http://screencast.com/t/pBELm1UE7LSo
If you need to append text - use CONCAT in expression
=CONCAT([x], 'some text after descr. ')OR
=CONCAT('some text before descr. ', [x])OR
=CONCAT('some text before descr. ', [x], 'some text after descr.')
Don't forget to set Description filed
see screenshot -
http://screencast.com/t/BaPdXCUe