essentially 
- You'd want to go to part_real_bonus guitar track.
- go to Track > Clone > From Track > select the 4 string path you did. (that way it clones everything like fhps/ tone changes etc.)
- go to Track > Pro Guitar > Set number of strings and set it to 6.
- go to Track > Rocksmith > Arrangement Type > update it to Rhythm Bonus (5/6 string bass charts are community accepted as Bonus Rhythm paths).
- go to Track > Pro Guitar > Set Tuning > set it so it's BEADGC (-5,-5,-5,-5-4,-4). (click No to the prompt that should pop up)
- ctrl + A to select all the notes > press up arrow to shift everything up so the notes are on the EADG strings.
- go through and move the notes you transposed down to the low B string. (and also remove any tone changes if they are still there since you won't need them here)
- double check your FHPs and update any that need fixing (I don't think they will need to be, but always worth double checking)
Then in the DLC Builder, you ONLY want to adjust the tuning pitch from A440 to A220. (you don't apply the low tuning fix on full 5/6 string bass paths, just change it from A440 to A220)
Then reminder when you get round to uploading the chart, it's nice to just make a note of what is on each path. When I do both a 4 and 5 string path, I usually put something like:
- Bass path has been transposed for 4 string players in E Standard playing some notes an octave higher.
- Bonus Rhythm is a full 5 string bass path in B Standard playing the low D notes.