Right now I compile my hacks and paste them into the ROM in a hex editor. Is there a way to just compile them into the ROM or something? (I work mainly on GBA stuff, so I'm using goldroad).
For GBA there is no way. You might want to write a small tool which inserts through batch file or something, still better than using a hex editor for it.
In a few years when I have time, I might extend xkas to work on any platform via the ability to manually specify your own address decoding inside the assembler file and/or opcode sets. Kind of like WLA DX, but again without all of the red tape.