ricky2014 - Windows 8/8.1 OEM will reload if placed on the same system, with minor changes [ram, gpu, hdd/ssd], not with moderate changes [motherboard/cpu].
For some countries, there's a tolerance for 2-3 activations on "diff" systems, but Slovakia is not among them, for sure
[tested it many times].
And when You re-activate Windows via phone, there's a preambula, where You have to agree with some official bs, and then it will on 99% let You re-activate even on new system. Worked many times for me.
But there are cases when they simply won't, and You have to send them a letter [real life letter, scan it/make a photo] and send it to them. Did that about a dozen of times.
Though, there's almost no chance You'll reactivate on new system via internet, without encountering activation issue.