You don't have to make it work on any of your carts,use DeSmuMe.
1)Transfer your .sav file from the root of your Cart to your Desktop.
2)Open DeSmuMe > Load your Pokemon Black/White > Click File > Import Backup Memory > Choose the .sav file you left on your Desktop.
3)Once the game is loaded just save your game,and close DeSmuMe.
4)Open DeSmuMe again > Load your Pokemon Black/White > Click File > Export Backup Memory > Save it in your Pokesav folder.
5)Edit the .sav file with Pokesav.
6)Open DeSmuMe > Load Your Pokemon Black/White > Click File > Import Backup Memory > Choose the pokesav'd .sav file > Make sure that you pokesav'd everything correctly/however you wanted > Save the Game > Close DeSmuMe > Open DeSmuMe > Click File > Load Your Pokemon Black/White > Export Backup Memory > Copy/Paste your .sav's name > Save it on your desktop(overwrite your old one if it's still there) > Transfer it back to your cart > Have fun.
I know i repeated myself a lot,wanted to make sure everything is clear.
Note : If Pokesav accepts your cart's .sav file,you can skip steps : 2,3 and 4.