Hi Chris,
Do you mean that the workflow is started, then the content changed, then the workflow resumed to send the message?
If you use Campaign v6 or v7, you can probably have a look at content validation mechanisms for deliveries. Though I'm not 100% sure that if a content is validated once, it is unvalidated after a modification. Would have to check that.
You can find more information about this feature here: Setting up marketing campaigns
If you use ACS, validation mechanisms are not implemented yet.
Let me know,
Florent