Yes, on 1.50. Use the attatched program and follow these steps:
Open MFAUDIO.EXE
Press open and select a valid audio file
In the "Output audio file" section, select the ".VAG" option and click "Save as", and save to an approprate place.
Install "X-Flash" onto your PSP. you can get it from
http://dl.qj.net
Place the .VAG file into your PSP, into "X:\PSP\GASE\XFLASH\XFLASH\MODIFIED"
There should be a file in there called "Coldboot.vag". Delete it, and name your custom sound to "coldboot.vag", or whatever the VAG file you deleted was called.
Boot up X-Flash, and find the audio replacement tool. Use option 5, and it will verify the file is valid, and replace the bootup sound.
I hope this works for you!