Yes, you can choose any veterinary clinic.
For the Comprehensive Plan, if you go to an unaffiliated veterinary clinic, you will be reimbursed up to 80% of the cost.
For the Basic Plan, you can go to any veterinary clinic if your pet has an accident, and they will reimburse up to €1,000.
In both cases, you will have to pay the costs first, and then request reimbursement.