Yes, Pre-Departure Test HealthCert results can be reused within the validity period defined by your destination country/region.
You may also reuse your Vaccination HealthCert. However, you will need to obtain a new Vaccination HealthCert if there is any change to the information reflected in your Vaccination HealthCert e.g. change in passport number, additional dose. You will also need to reissue your Vaccination HealthCert if your current certificate only has the online QR and you require the new EU Digital COVID Certificate-compatible offline QRs (from 7 December 2021) for travel.