%HRMax range as training target

My training plan tells me to do workouts e.g. in 70-75 %HRMax range or 80-85. Is there a possibility to define those ranges as training targets? AfaIk it is only HR Zone or defined HR range. The latter I could calculate of course. However, if my HRMax changes, I have to adjust all trainings accordingly…

Does anyone know if it is hidden somewhere and I missed it? Or is it not implemented and you would love to see this feature as well?