blocking out thoughts for a useful animation curve utility

anim_curve_anchor.py

start_time = 0
end_time = 10


keyed_channels = get_keyed_channels()

for curve in keyed_channels:
  #what is the best method to select the target keys?
  #select keys in range(start_time,end_time)
  first_key_value = 3
  anchor_key_value = 1.5
  offset_value = anchor_key_value - first_key_value
  
  keyframe -animation keys -relative -valueChange (0 + offset_value) ;