Installing Windows 7 Home on an existing Windows Professional

I leave my workplace soon, and I have the opportunity to buy my computer. Whether it is a good idea or not, that's up to me, but what I am interested in is to keep my data, softwares, preferences, etc. I want to precise that there is no critical data on the computer and I can safely get it out of my workplace, there is nothing wrong with it.

The version of Windows that we have is a Professional license, where I need to be connected once in a while to the network in order for it to work. I would like to downgrade to Windows Home Premium.

The IT guys tell me that they have to do a complete re-installation of Windows, thus losing all my data/softwares. This solution does not suit me at all and I am in search of an alteative.

I have found this superuser thread, but I guess the IT guys will be reluctant to use a non-supported software (official policy, blah blah).

Can I follow those steps:

1) Run the Windows Home installation disc and choose "Upgrade" and let the magic happen.

OR

2) Run the Windows Home installation disc and choose "Custom" and install on the Windows Professional partition. I have read that Windows will rename the existing Windows version windows.old, it will be unusable, but all the registry keys will remain. Am I wrong ?

Of course, the IT guys will do a complete clone of the drive, in case anything goes wrong.

Thanks a lot for your answers,

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