A patch contains work that YOU did, not Rare. Since you're just sending the work you did across the web, it's perfectly legal.
I hate it when people ask me how to patch a rom too. It's so damn annoying. So here are my VERY specific instructions (Taken from ReadmeNOW.txt) on how to patch this.
Creating a patch.
A. Download this:
http://www.zophar.net/utilities/download/lips100.zip
B. Download a clean Banjo-Kazooie (U) ROM. I do not give links to ROMs, just do a google search and in about 5 minutes you'll find it.
C. Open up Lunar IPS, and click on the option "Create IPS Patch"
D. Select the ORIGINAL UNMODIFIED ROM (Which would be, the clean Banjo Kazooie (U) ROM.
E. Then, select the ROM that you modified.
F. Name your IPS, and save it in the folder.
G. You have created your IPS file. Bravo, you're a freaking genius.
Applying a patch:
A. Download this:
http://www.zophar.net/utilities/download/lips100.zip
B. Download a clean Banjo-Kazooie (U) ROM. I do not give links to ROMs, just do a google search and in about 5 minutes you'll find it.
C. Download a Nintendo 64 Emulator, again, USE GOOGLE.COM
C. Use Lunar IPS.exe, click "Apply IPS Patch"
D. Select the patch, which is - (What ever your name is).ips
E. After it will ask you to select a ROM. Find the Clean Banjo-Kazooie (U) ROM.
F. Use the emulator to open the ROM. If it has the changes applied, congratulations - your IQ is at LEAST above 25 points.