Can exterior french door installed to open in be changed to open out?

Maybe.

The primary issues are likely water and security.

Exterior doors that face outward need to have properly detailed heads and sills to prevent water migrating inwards. If the door wasn't specified this way when it was manufactured, it is likely that you will have an issue here, unless it opens to a fully covered porch or other space where precipitation is not an issue.

Also, when the doors face outward, the hinges do, too - which means the pins can be easily removed from the outside and the door thus removed, without a key. Special hinges are made for this and can usually be retrofitted easily enough.

Lastly, the glazing needs to be considered - check that the seal is weatherproof - it may be detailed differently on the interior and exterior sides of the door. This may be especially true if the door has muntins.