Yes you can and it doesn't even take that long

Easy method: use the World of Goo Profile Renamer

Manual method:

Step 1: BACK UP YOUR pers2.dat file. Where is it? Look here:

You can also use the "Backup" button on GooTool's "Profile" tab, but I recommend taking a safety backup by hand as well.

Step 2: DECRYPT your pers2.dat file (GooTool -> Advanced menu -> Decrypt -> .bin (Windows/Linux).

Step 3: Edit the decrypted file. Search for your name and edit it. Note down the number of letters that you add or remove. For example, changing "davidc" to "wibblewob" is +3 characters. Changing "davidc" to "god" is -3 characters.

Step 4: Immediately before your name you'll find a (possible big) number. For example, mine reads "...mrpp1,09,profile_017024,davidc,31,372011...". Add or subtract the number of characters you changed in step 3. For example, changing "davidc" to "god", I'd change 17024 to 17021 because I removed 3 characters.

Step 5: Encrypt the file using the Advanced menu again. Save it on top of your old pers2.dat.

Load World of Goo and your name should be changed. If it failed or if you have lost your profile, restore from backup.

Hope that helps. I don't intend to add this to GooTool, for the same reason that I don't intend to add fullscreen preference to GooTool: I don't want to add anything that can amend a user's profile file (pers2.dat).