Total_Noob has released an update to CXMB, which now has compatibility with firmware versions 3.71 up to 5.50. CXMB allows users to use custom CFT themes without the risk of flashing your flash0.
Changelog:
-This version of CXMB works for custom firmware’s:3.71-5.50
-Its a Full version so you can also use it to make ctf’s,
make sure you [...]

PSPGen have released CXMB for Custom Firmware 5.50 GEN-A, while its still in a beta stage it will allow 5.50 GEN-A users to use CXMB CTF themes. Its an unofficial version of Poison’s CXMB. It also loads the CTF themes without touching your PSP Flash memory, which is risky.
Source: PSPGen (French)

Homebrew developer Poison has released an update to CXMB his cfw plugin which allows users to load custom CTF  PSP themes. And all from the memory stick and not the flash memory so there’s no risk in bricking your PSP. This release add’s 5.00 M33 support, nothing else has changed.
Source: 2Alien.info