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I believe the ‘within 10 days’ language is for after the exam.
CFA Institute used to offer refunds if you test positive within 60 days of your scheduled exam, but this is no longer the case, and the new policy is within 14 days:
If you have been diagnosed with COVID-19 in the 14 days leading up to your exam appointment, have been exposed to someone diagnosed with COVID-19 in the 14 days leading up to your exam appointment, or are exhibiting symptoms of COVID-19, you must not report to the test center on your exam day. Instead, contact us for more information.
I would test again within 14 days and if it comes up positive, get in touch with CFA Institute and you should be able to get a deferral.
Good luck, and let us know how it goes!