Is it permissible to register at a training center to benefit from student transportation discounts rather than for study?

This depends on the condition set by the entity granting the discount. If it stipulated that the beneficiary must be a student currently enrolled in studies, then you are not entitled to it unless you meet that condition. However, if the entity did not stipulate that the beneficiary must be regularly enrolled in studies, then you may take it as long as you are deserving of it, without deception or cheating, for the Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions."