It is not legal for a pharmacist to simply alter a doctor's prescription. They are not allowed to do that.
But a good pharmacist might notice an error in the prescription as written (perhaps a conflict with another drug the patient is taking) and contact the doctor for corrections or to verify a prescription. A new prescription can be issued.
With prescription errors, human error definitely plays a role. Errors can be traced to a pharmacist's misreading of a doctor's handwriting. There can be data entry errors.
Your goal should be to get your medication and, if the pharmacist erred in filing your prescription, the error could be reported to the Pharmacy Board later.
Maryland Board of Pharmacy complaints:
https://health.maryland.gov/pharmacy/Pages/complaint.aspx
Because prescriptions are generally entered in a national database, if one pharmacy won't fill a prescription, other pharmacies may not fill it either.
Good luck.