Using well-established abbreviations for new concepts in the same field Should a researcher try her best to avoid using existing abbreviations (such as IEEE, WHO, DNA, ANOVA, BMI, CERN, NASA, UNESCO, OPCW, NHS, CDC ...) that are (well-)known in her fields, when creating abbreviations for new concepts (methods, substances, studies ...) in the same field?

Or is it OK if the abbreviation for the new concept is just defined where it is used (e.g., in a publication)?
Yes, you should avoid using well-established acronyms to mean something else. I would especially avoid those like the ones you present as examples that are likely more recognizable as the acronym than what the acronym stands for: they are effectively words by themselves with a specific meaning.