Reinstalling Windows 8.1, new motherboard install

[GangstaRas]

I just want to make sure of something. I currently have Windows 7 on the primary drive and would either do a clean install or upgrade to Windows 8.1. I bought the retail version of Windows, not the OEM version. The system currently working with the Windows 7 is an old system that I'm actually in the process of upgrading (mobo change to an entirely different platform). So I ask for a confirmation in 2 different scenarios. If I upgrade my Windows 7 to Windows 8.1 now on the old system with the old motherboard, if I change the board, will I have any complications of invalid Windows key and all kinds of crap after? And will I be able to install Windows 8.1 on a secondary hard drive I have should I see fit?

 

I take all answers but I would prefer someone with Windows 8.1 retail version answer me if they have been in this situation and have the experience of what happens. I don't really want a "it should work" kind of answer