So! You’ve seen some stepmania 3.9 videos, thought it was cool and wanted to “recreate” the experience in etterna by just using the 3.9 noteskin. Awesome. I did the same thing. However, since you don’t play upscroll like in those videos, you try using it regularly with on downscroll and notice that holds are broken!!
As it turns out, old noteskins like these (i’m using note as my example, as in the image above) were specifically made for upscroll, which you could realize by looking at the skin’s metrics.ini:
#Edit this incase you want to make noteskin for reverse or both FlipHoldBodyWhenReverse=0 FlipHeadAndTailWhenReverse=0 TopHoldAnchorWhenReverse=0
“or both” is what implies that you can in fact make a noteskin that works for both out of the box, which is the majority of noteskins nowadays, but this is 2005, and note was made for upscroll only.
Thankfully, editing this noteskin to work with downscroll is easy. That little snippet of code from metrics.ini that I’ve pasted above is almost everything you need to "fix" the noteskin so it works on reverse: Just change those three 0s to 1s. The metrics.ini file is located on the noteskin folder:
After making the edit, you can reload the noteskin by pressing F2 in-game. This will lag a bit as the game reloads a lot more stuff than just noteskins. But once it’s done, voilá!
But those with a keen eye might already notice there’s something wrong:
something wrong
HOLD ENDS FOR UP AND DOWN AREN’T RIGHT!!! AAAAAAAAHH!!!
This is, without a doubt, a really annoying detail that you will notice during gameplay, and fixing it is a step above just changing zeroes into ones: Now, you’ll have to change filenames. 
There’s a whopping total of 16 files that must be renamed, the exhaustive list is as follows:
| Rename this… | …to this |
|---|---|
| Down Hold Body Active.png | Up Hold Body Active.png |
| Down Hold Body Inactive.png | Up Hold Body Inactive.png |
| Down Hold BottomCap Active.png | Up Hold BottomCap Active.png |
| Down Hold BottomCap Inactive.png | Up Hold BottomCap Inactive.png |
| Down Roll Body Active.png | Up Roll Body Active.png |
| Down Roll Body Inactive.png | Up Roll Body Inactive.png |
| Down Roll BottomCap Active.png | Up Roll BottomCap Active.png |
| Down Roll BottomCap Inactive.png | Up Roll BottomCap Inactive.png |
| Up Hold Body Active.png | Down Hold Body Active.png |
| Up Hold Body Inactive.png | Down Hold Body Inactive.png |
| Up Hold BottomCap Active.png | Down Hold BottomCap Active.png |
| Up Hold BottomCap Inactive.png | Down Hold BottomCap Inactive.png |
| Up Roll Body Active.png | Down Roll Body Active.png |
| Up Roll Body Inactive.png | Down Roll Body Inactive.png |
| Up Roll BottomCap Active.png | Down Roll BottomCap Active.png |
| Up Roll BottomCap Inactive.png | Down Roll BottomCap Inactive.png |
On Windows, this task is made easier with the usage of PowerToys’ PowerRename:
Keeping in mind that you need to run it once with a dummy name temporarily so that filenames don’t conflict.
If you’re on Mac/Linux, you’ll figure something out. I trust in you 
After renaming everything and hitting F2 again to reload the noteskin, this is the result:
And congratulations
, you’ve made an old noteskin work for your downscroll needs.
Addendum
I’ve skimmed over the noteskin’s .lua files and metrics.ini to see if instead of renaming these files I could just make a simpler edit (compared note with midi-note) but I didn’t find anything that my noob brain could comprehend. If it’s possible I’d like to know.