First, cross posting is a big no-no here. Beware.
Technically, you could do the install, but you'd be replacing your PIN and info on your computer's desktop manager with his. You could then go BACK and do it to your's again, but it would be a bit of a pain...I probably wouldn't want to do it. Depends on how good of a friend they are.
If you delete the Vendor.xml file before the install, and replace the Blackberry.alx file (as instructed in a couple places on this site), the install will be find on his handheld, and all the themes available for that release will be there.