You may alter them all you like, after all, those are the values that you are allowed to edit. But, unless the hidden values are identical with the current values for those fields in the database, the update will not happen.

That means that, for the update to take place, that either you have to not touch the hidden values at all, or, if the record got updated in the meantime, you must know exactly what you're doing, and manually fill in the new exact current value for those fields.

I agree that it's a bit of an overkill, especially for long strings, to send the same data to the browser more than once. After all, just sending a CRC or digest value (MD5, SHA1,...) would suffice, for the check.