90-day licenses are ONLY issued as trials, and require a reformat and reinstall (using appropriate media) before a perpetual license can be installed.
KMS licensing is a bit of a minefield - there are a lot of hoops which have to be jumped over.
1) You have to purchase the KMS server license, set it up and activate it.
2) you have to have AT LEAST 25 clients ( or *I think* 5 servers) using Client Keys and connecting successfully, before the server will start issuing licenses.
3) Clients (at least) must have valid SLIC tables for a qualifying OS - or no SLIC table at all. If the SLIC table is damaged, then that machine must use an MAK Key.
All KMS clients reactivate every few days against the server - if reactivation doesn't happen within 180 days, then the system will throw a wobbly, and show as non-genuine. This means that it's often not a good idea to have off-site machines using KMS activation.
The use of a Loader (AKA Activation Exploit) AUTOMATICALLY renders any system on which it is installed 'counterfeit' - even if otherwise the system would be considered genuine - since it breaks the Licensing Agreement to which you agreed when first installing Windows, by attempting to circumvent activation and validation requirements.
KMS activation will react in much the same way as ordinary activation to a change in hardware, and demand full re-activation in the event of a major hardware change. I *know* that simply changing the MAC address of a NIC adapter is sufficient to require this - although a lot of other changes don't. Since changing the motherboard almost always means a change in MAC address, (it also changes other details, which could also force a reactivation request), there is no way to change motherboard without triggering reactivation - and changing the KMS counts one way or the other.
If you want serious detail on KMS and what you can and can't do with it, then you should ask in the MS ITPro forums here....
Technet forums - Windows 7 Installation, Setup, and Deployment
If you are an MS Partner, or TechNet/MSDN subscriber, then you will get an 'official response, as well as any 'practical' response from other users.
