Yes, you can change it to something custom.
You need CFW to access your PSP's flash0.
Do not MESS with files unless you know what you are doing.
Get a pandora if you want to mess around but remember not too much.
You will need a coldboot file. Download one by "googling".
Tutorial :
Video :
YouTube - How To Put Custom Coldboots On PSP
Text :
~Ace Dawg's Guide to Easy Flashing of Almost Everything on 3.03 OE & 3.10 OE!~ - PSP®General - PlayStation.com Forums
*Get the right opening_plugin.rco for the firmware of your PSP and it will work with M33 as long as you have the right opening_plugin.rco.
*THIS MAY BRICK OR SEMI-BRICK YOU PSP. SO GET A PANDORA HANDY. Really.
Tips and hints:
Don't get frustrated when you enter flash0 and ZOMG too many files!!! Ill delete them! Seriously don't :P
Those things should guide you.
Hope it helps!