Yes, its possible. I already did this with some of my injections, like Parasite Eve, Earthworm Jim 2, ect. (On PE you can listen the first seconds of the intro, on EJ2 you can listen Jim saying: Groovey!)
@Asdolo recently released NSUI Debug Beta 28, that includes PS1 injections, and with that you can customize icon, banner and the sound banner. The problem is that Asdolo is not working anymore on NSUI (it a shame, but he has a life, he explain why on this thread: and he incorporated the PS1 injections on 2018-12-26, so it uses and old version of PCSX REarmed. (And belive me, PCSX RE improves a lot the last year, thanks to
@justinweiss )
With the PS1 Forwarder Creator of
@Sakitoshi , you have an updated Retroarch Forwarder (it not includes the experimental Hi-Res Downscaling option that justinweiss include on a 3dsx a few weeks ago), but for replace the sound banner you have to do it manually. You have to replace the ps1.wav file on the assets folder (PS1 Forwarder Creator\tools\assets_ps1) (Also, you cant have different images for the icon and the banner like on NSUI, PS1 Forwarder Creator uses the same image for both. Still, PS1 Forwarder its great and works better because it use the most recent PCSX RE as core)