Installing FCP 7 on system that has FCP 10?

Funky situation. I'm trying to help a friend here, who hasn't used the Forum before.

He's just completed shooting his first film. He bought and installed FCP X. And then hired an experienced editor who works in FCP7. The editor tells him the project is too complicated to edit in FCP X in the time span my friend is requiring. My friend wants to work with this particular editor. So he then bought a copy of FCP Studio (from Amazon.com I believe). He did an install. All the ancillary apps like Color, DVD Studio Pro, installed just fine ... but the FCP7 option-to-install is grayed out.

He wants to edit in his own studio, and have access to all the work after the editor is gone ... thus he wants to have FCP7 on HIS own system for awhile.

I'm thinking the FCP Studio install discs are seeing FCP X sitting there, and thus have automatically grayed out the FCP7 install choice.

Two questions:

Am I correct in my assumption? If so...

1. Can he un-install FCP X? (And the best way to do this?)

2. Will this allow FCP 7 to be installed (meaning the FCP7 install choice is no longer grayed out in the install process)?

3. After the deadline for the film is met, and the film finished, he eventually wants to go back to FCP X. He purchased FCP X from the Apple Store as a straight download and install. Can he then remove FCP 7 and re-install FCP X from the Apple Store, without having to buy another FCP X license? (I had trouble with an install download once, and was able to re-do the process through the Apple Store, no problems.) What would he need to have to be able to do the re-install of FCP X when this is all over? He is visiting at the moment, and far from his office, and can't remember if FCP X as a download install from the Apple Store came with a serial number. (I suspect it's in an email from the Apple Store, but can't remember myself.)

Any help would be most appreciated,

Ben