Keep in mind a few things:
1) A change like that could (will?) cause your ticket number to reissue. That could cause auditing problems and they may find out anyway.
2) Just because it was emailed to you doesn't mean the company TA doesn't also have notifications and/or access to the ticket, and they may find out anyway.
3) Ensure that your modified ticket has the same fare rules including change or cancellation fees, in the event business plans change, and doesn't violate company policy.
4) Does company policy allow for a stopover?
5) What if there are IRROPS on day of travel and you miss your business meeting due to a weather in Tokyo, or can't get back to the airport on time due to any number of reasons?
6) Routes are subject to change, your contract is just for origin and destination, so you may still not end up in Tokyo but now have gone to expense anyway.