Can I use different transports based on X-header or address extension?

Hello, I've got a requirement to configure our mailserver to deliver
certain email messages "normally" (e.g. to the recipient's MX record),
while other messages need to be sent to a 3rd party relay to be
delivered.

The easiest thing for us to do would be to use an address extension,
or add an X-header that the receiving postfix would see, and make a
decision on the transport to use.

In other words user+foo@domain.tld would be relayed to our third party
email relay, whereas user@domain.tld would be sent "normally". I would
also need to strip off the extension before relaying to the 3rd party.

Is something like this possible with postfix?

thanks,
cross-eye