All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
What you have mentioned about violating the terms and conditions of the insurance companies and lying about this is forbidden and not allowed in principle, and the Muslims should honor their conditions. The Prophet said, “Muslims should fulfill their conditions.” [Abu Daawood]
The fact that some optical shops accept to provide sunglasses instead of sight glasses or lenses does not make it permissible if the insurance does not authorize it and does not cover it.
The same thing applies to the insured person buying things for others, or even for himself if he does not need it.
Allaah knows best.