Is it permissible to recover the cost of a fictitious air freight invoice to benefit from the price difference in sea freight?

If the amount granted to the student is a lump sum that the student owns, regardless of the shipping weight, then there is no objection to the student freely shipping their belongings and benefiting from the difference. However, if the amount is given based on the actual weight of the baggage, then the student is only entitled to the value of the sea freight, and must return the remaining amount to the employer. This is because, in this case, the student is an agent for the employer, and an agent only acts within the scope of their agency, and any excess reverts to the principal.