The specific answer to your question is no, you can't alter any form values if validation fails. To implement this, you'd need to let the validation succeed and let the data get modified. As part of the validation/modification, you could set a piece of page state that causes the next loadData
pass to display the "is this the word you meant?" message near the spell-checked form item. Of course, you would have already saved the corrected text.
Alternatively, you could use PostBack.CreateIntermediate
to make a post-back that only runs the spell-check, puts the corrected text in page state, and displays "is this the word you meant?". You'd set that post-back to fire when the user tabs out of the text box, and then you'd have the main post-back grab the corrected text from page state and save it in the database or other durable storage.