You mean I can call an automated telephone number and it will give me a new code?
Activation code (which is actually what "unlocks" the copy of Windows), not License code. The License code always stays the same. The Activation Code links that License code to a particular installation of Windows, and turns it on.
In theory, they could track how many times you've used a particular license, and prevent you from re-activating it (the OEM copies are licensed for only the physical hardware you install it on, and you aren't allowed to move them to a different motherboard, for example). But, in practice, if you call, and read the dumb automated thing the huge string of numbers the Activation wizard gives you and then say "one" when it asks how many computers this copy of Windows is installed on, it will give you an Activation Code.
The system is just designed so that they can "retract" License keys that leak widely, and permanently disable those. So, if you called with Some License Code You Found On The Interwebs, that'll be just disabled and it'll probably put you through to a person. With a regular person's kind of usage (even a nerd who moves things around all the time like me) you can just call and it'll give you the Activation code you need. Annoying, but it works.
Only thing is, though, it took MC Mac 5 hours to update 15,000 files while on the Windows side it took maybe 30 minutes.
Yeah, the first thing (writing from the Library to the Files) is slow. That has to look at each file on disk, and then actually write the ones where tag data doesn't match the Library. The reverse is much quicker, because it is just reading from disk and writing to the (ultra-fast, that's the point) Library in memory.
You probably didn't need to do #1, actually, because MC automatically keeps the tags in sync when you make changes, unless you deactivated that option. It doesn't hurt, and forces them to be in sync, but they probably were mostly already.
I have a problem on the Windows side now running the MC Media Server and MC GUI at the same time. I get GUI crashes when trying to edit tags while paying music; Windows gives error message suggesting you can't run Media Server and MC client at the same time. If I shut down the client and just have media server running I get strange behavior like failure to play a complete playlist. So i just run MC client without the server and everything seems fine. What do I need that server for? Running other instances of the client on other PCs?
That's a good question, but it is probably best to start a new thread on it.
I will say this, though... The difference between "server" and "client" isn't as defined as you're thinking it is. The Server IS a Client is a (or can be) a Server. You can even turn on the Server of a Client of another Server (which is handy for remote control sometimes). Both functions are done by the same EXE, though.
Are you trying to run multiple copies of MC for some reason? Generally, you should NOT be, and MC won't let you.
All you need to do to enable MC's Always-On server mode is to enable the Media Network stuff in Options, and then go to
Options > Startup > Windows Startup and set it to either Media Server or Media Center and Media Server. To be clear, MC's Server isn't designed to run as a Service (without any user logged in on the console). You can hack it to work that way, but it isn't designed that way, and you could encounter problems.