To change stuff like that, beyond what you can do with installing a home replacement app, you need to root.

 

The one I used is How To: Root the Nexus One (Updated 01.11.10) | TheUnlockr - there is text and video to follow, so you can't really go wrong.

Follow the instructions slowly, be most careful when flashing a new radio!

 

Try this method, it's what I did.

[How-To] ROOT Your Nexus One without Unlocking the Bootloader. ALL ROM'S!! - Google Nexus One Owners | Google Groups

Hope this helps!

 

I was on FRF91 (latest official 2.2) and it worked (use the link I posted above)

 

I used this last night, easy, perfect!

 

awesome! :d

 

Think I'm going to do this today with your guide if I get time.

Do I need to backup everything on my phone first?

 

Nope, it shouldn't delete anything on your phone or anything. I'm taking the plunge now.. Downloading Android SDK 2.2 as we speak.

 

No wipe if you just ROOT only...

If you install custom recovery and ROM, yes, it WILL WIPE.

All, if you are using the guide I posted (I am always editing it) please give feedback if anything is missed and I will correct it.

The original guide is not mine (I linked the source) but I hosted it on my google group because it gives me a chance to have an external place to store it in case the original thread vanishes, and I can add additional hosts for the files.

Not to mention that I can add my own insights and others without having to bug the OP on XDA.