Will the clean install of Win 7 mess up the boot manager or whatever such that I will be unable to recover the original factory installed Win 8?
Yes, it might.
You will have no trouble installing 7 to the win8 partition - leaving recov partition intact.
It depends how the oem set up accessing the recov proram.
There are a couple of ways round that.
First, make an image of the win8 partition- and the system partition. You can use any number of free tools for that.
If it is gpt - try the paragon backup and recovery free.
Second, run off a win8 repair cd/usb.
If the oem has a standard wim file in recov partition, you can boot the win8 repair cd and use system reset to apply the wim. Or you can use imagex/gimagex/any other wim handler.