ive never installed cxmb on a psp with cfwenabler 3.60 personally, but this is what i suggest.
you can download cxmb for 5.00 m33 from here:
CXMB for 5.00 M33 Released, PSP Hacks - PSP Slim Hacks
this download comes with a "lite" version that doesnt mess with you flash0.
just download, unpack, and merge the contents of the lite folder to the root. after that, you need to add the line "ms0:/cxmb/cxmb.prx 1" to your vsh.txt. you may need to go into your recovery menu and enable the plugin as well.
after that, you can try running a custom theme. they must be in .ctf format, and need to be placed in the ms0:\PSP\THEME directory.
it may not work, but it wont brick your psp either. just give it a try.