In PS5 Scene news following the initial Custom BGM & Themes PS4 PKGs, PS4 Theme Sample & Base Template, BD-JB PS5 ELF Loader v1.2 and PS5 System Partition Read / Write (R/W) Payload comes some demonstration videos of the first Custom PS5 Themes including Background Music (BGM) of Hyperdimension Neptunia Theme v0.9 Beta from Ifaicompa (NepuStation3322's YouTube Channel) alongside a PS5 Just Do It Theme (PS5 BGM Change) from @yyoossk (Twitter / Yyoossk7821's YouTube Channel), a PS5 Elden Ring Custom Theme with PS5 Partition Mount (PS5PM) ELFs from @ifcompass (aka Ifaicompa), demo and Custom PS5 Theme Tools below from @master s9 via Twitter. 
Also below is a NMount PS5 System RW Source from Decompiler via @zecoxao on Twitter for those interested in source code examination of the recent PS5 system/system_ex R/W mounting.
From Pastebin.com: nmount PS5 system rw source from decompiler
The first custom theme for PS5
PS5 Partition mount (PS5PM) [The first PS5 custom theme] This payload will mount /preinst /system /system_data /system_ex /system_tmp /update partition directory as R/W
PS5 Just Do It Theme
PS5 Partition Mount v1.2 (PS5PM v1.2)
you can't also access those partitions from the /dev/ system, only the other 11 ones. So, which partitions are these 2? Needs more research...
it is theorized that the coreos is present inside the ssd, so maybe these two partitions have something to do with it...
For users who do not use Telegram:

Also below is a NMount PS5 System RW Source from Decompiler via @zecoxao on Twitter for those interested in source code examination of the recent PS5 system/system_ex R/W mounting.
From Pastebin.com: nmount PS5 system rw source from decompiler
Code:
__int64 __fastcall _payload_base(_QWORD *arrayPointer, unsigned int *lengthPointer, __int64 string1, __int64 string2)
{
__int64 functionResult; // rax
_QWORD *str1Ptr; // rbx
__int64 strdupStr2; // rax
__int64 strlenStr2; // rax
int v10; // [rsp+2Ch] [rbp-14h]
int v11; // [rsp+2Ch] [rbp-14h]
functionResult = *lengthPointer;
if ( (int)functionResult >= 0 )
{
v10 = *lengthPointer;
*arrayPointer = realloc(*arrayPointer, 16LL * (int)(*lengthPointer + 2));
if ( *arrayPointer )
{
str1Ptr = (_QWORD *)(*arrayPointer + 16LL * v10);
*str1Ptr = strdup(string1);
*(_QWORD *)(*arrayPointer + 16LL * v10 + 8) = strlen(string1) + 1;
v11 = v10 + 1;
if ( string2 )
strdupStr2 = strdup(string2);
else
strdupStr2 = 0LL;
*(_QWORD *)(*arrayPointer + 16LL * v11) = strdupStr2;
if ( string2 )
strlenStr2 = strlen(string2) + 1;
else
strlenStr2 = 0LL;
*(_QWORD *)(*arrayPointer + 16LL * v11 + 8) = strlenStr2;
functionResult = (__int64)lengthPointer;
*lengthPointer = v11 + 1;
}
else
{
*lengthPointer = -1;
return perror("realloc");
}
}
return functionResult;
}
int __cdecl main(int argc, const char **argv, const char **envp)
{
unsigned int v4; // [rsp+4h] [rbp-Ch] BYREF
__int64 v5; // [rsp+8h] [rbp-8h] BYREF
v5 = 0LL;
v4 = 0;
_payload_base(&v5, &v4, (__int64)"fstype", (__int64)"exfatfs");
_payload_base(&v5, &v4, (__int64)"fspath", (__int64)"/system");
_payload_base(&v5, &v4, (__int64)"from", (__int64)"/dev/ssd0.system");
_payload_base(&v5, &v4, (__int64)"large", (__int64)"yes");
_payload_base(&v5, &v4, (__int64)"timezone", (__int64)"static");
_payload_base(&v5, &v4, (__int64)"async", 0LL);
_payload_base(&v5, &v4, (__int64)"ignoreacl", 0LL);
if ( !(unsigned int)nmount(v5, v4, 0x10000LL) )
return 0;
perror("nmount");
return 1;
}
PS5 Partition mount (PS5PM) [The first PS5 custom theme] This payload will mount /preinst /system /system_data /system_ex /system_tmp /update partition directory as R/W
- ELF & Theme Downloads: PS5 partition mount & custom theme (PS5 partition mount & custom theme.zip (108 MB) - includes PS5 Single Partition Mount Payloads: preinst.elf, system.elf, system_ex.elf and update.elf with PS5PM_v1.1.elf alongside Theme files PS5 Hyperdimension Neptunia Theme v1.0.zip and PS5 Hyperdimension Neptunia Theme v1.1.zip)
- Source code from: John Tornblom
PS5 Just Do It Theme
- PS5 Just do it thme.zip (31.3 MB)
- PS5 partition mount & custom theme.zip (185 MB - includes getpid.elf, mntinfo.elf, PS5 BD-JB ELF Loader v1.2.iso, remount.elf, preinst.elf, system.elf, system_ex.elf, update.elf, PS5PM_v1.1.elf, PS5 ELDEN RING Theme v1.1.zip, PS5 Hyperdimension Neptunia Theme v1.0.zip and PS5 Hyperdimension Neptunia Theme v1.1.zip)
- Theme file can be directly overwritten into the corresponding directory to take effect
- PS5_chainsaw_man_makima_custom_theme.zip (73.2 MB)
- PS5 payload loader.zip (48.9 KB) / Live Demo
- PS5 ThemesV1.00.Test.rar (171.49 MB - includes PS5 Themes.exe)
- PS5 ThemesV1.03.rar (184.91 MB)
- Payload⭐.zip (3.1 MB - includes preinst.elf, PS5PM_v1.1.elf, system.elf, system_ex.elf, update.elf, hardware_information.elf, list_all_files.elf, list_logs.elf, pipe_pirate.elf and process_view.elf)
- PS5 Theme Cyberpunk 2077 Multi-font version 1.0.zip (498.8 MB) / PS5 Theme Cyberpunk 2077 No Font No ⚡ Logo Version 1.0.zip (496.7 MB) / PS5 Theme Cyberpunk 2077 No Font Version 1.0.zip (496.7 MB) / Mega Folder
- PS5 Theme God of War Ragnarok - Raiden.zip (310.9 MB)
- PS5 Theme God of War - Burning Rage.zip (331.7 MB)
- PS5 ThemesV1.04.7z (224.99 MB)
- PS5 Theme God of War Ragnarok - Raiden.7z (288.2 MB)
- PS5Themes_GodofWarRagnarok+Font_V1.0.5.7z (393.6 MB)
PS5 Partition Mount v1.2 (PS5PM v1.2)
- PS5PM.v1.2.elf (649 KB)
- PS5ThemeFire.7z (139.86 MB)
you can't also access those partitions from the /dev/ system, only the other 11 ones. So, which partitions are these 2? Needs more research...
it is theorized that the coreos is present inside the ssd, so maybe these two partitions have something to do with it...
For users who do not use Telegram:
- PKG: Theme_Ps5_Qz.zip (72.9 MB)
- ctmthm: Theme-ctm_PS5_Qz.zip (31.3 MB)