Is it permissible for an employee to purchase a computer with an amount allocated for their professional development, then return it to the store and reclaim its price, if the company allows the purchase of a computer only once?

You are not permitted to benefit from the money except by purchasing the computer and using it for the purpose stipulated by the employer. This is because violating the conditions constitutes lying, deception, and unlawfully consuming people's wealth. The Messenger of Allah, peace and blessings be upon him, said: "Muslims are bound by their conditions," and "The wealth of a person is not lawful except with his willing consent." Furthermore, the company stipulates this for a benefit that accrues to it, and this resembles a gift of reward. If the purpose is not achieved, the giver has the right to revoke his gift.