In the en file located in the ~/Library/Spelling directory you’ll find any custom entries into the Mac OS X dictionary. Each will be followed by a ^@ and there will be a final one with no characters at the end. You can remove entries by removing the word followed by the ^@. You can also add items into the custom dictionary by adding the word at the end of the en file along with a trailing ^@. Each item is stored in the order that it was added and so you can also gain a little insight into when each word was added.
So, if you push out a custom dictionary file as part of your image as I did recently and a wrong spelling of the word science, you can then push out the en file or a script to just remove the offending entry (along with the trailing ^@) from the en file. You can also build custom files with commonly used words for your environment and push it out, either to default profiles or to a users ~/Library/Spelling/en.
