Colleges will typically only accept final transcripts directly from the HS. What is the difference if the HS mails the final transcript or the student? Regardless check the rules of the college you are asking about.
Most HSs have policies and procedures in place that ensure only one final transcript is sent for graduating seniors as thumper said. So, if a college accepted a transcript in a sealed envelope mailed by the student…the HS is still only going to give your student one of those.
HSs will send a second final transcript for schools if a student gets off a waitlist. Probably this year a school would send a second transcript to a June 1 deadline school, if the student deposited elsewhere earlier, and changed their mind.
Either way the student has to withdraw their enrollment at the first school they deposited to, and will likely forfeit the deposit money.