I do believe Rudolph created a Slot 2 GBA Dumper but I cant remember if it can redump a ROM onto a retail cart like his Slot 1 Dumper. I'll go check.
EDIT: OK, so I just downloaded Rudolph's GBA Backup Tool v0.21. I believe what you want to do, is 100% do-able.
1) Download
GBA Backup Tool v0.21 by Rudolph.
2) Place GBABackup_Tool.nds & GBABackup_Tool.ini onto your Acekard.
3) Place you original GBA Cartridge into Slot 2 & Launch GBA Backup Tool and hit (A) on the first Pop-Up
4) Once the ROM Info appears, toggle ( R ) until you see the Bottom Window in the Bottom Screen turn from "Save Backup" to "Rom Backup"
5) Hit (B) to create a new GBA File.
6) Turn off your DS once it finished and replace the original with Hacked GBA ROM in the GBA_Backup folder the the GBA Backup Tool created.
7) Eject MicroSD & Launch again from Acekard, this time when you toggle from "Save Backup" to "ROM Backup" , the first option will darken which is the option to update the current GBA ROM. (A)
The Hacked ROM can be named to anything, I do believe.
I tried this app with Pokemon Leafgreen and it dumped perfectly.
~ Jon
Have Fun!