You can still do it manually.
Link to middle of page 2 of thread where the explanation starts. Get as close as you can in Customise, then Show Changes, then edit the file to remove the filename from ClothingLegMap= (and replace it with the filename of your chosen frilly knickers or whatever if you want them), save the file, click back to RLC and Cus => Don't Change => Cust => Show Changes to load your edited version onto the avatar.
Like it says in that thread, make a backup .ini first and make copies of myinfo.ini for various outfits so you can copy them to quick-change.