So one thing I found that works well for this is the following:
1 In Rekordbox select the file you want to use in another playlist
2 Right Click and open the file location
3 look at the filename and change one character from upper to lower Case (or vice versa)
3a. Note that this doesn't Change the Filename except to Rekordbox.
4 Drag the File to your new playlist
5 set Hot Cues and Memory as you wish
Rekordbox now has 2 different entries for the Same file! I use this all the time if I want different beat grids or Cue points for the same track. Works great and no additional copies of the same song.
Hope That helps!