Warning, this is greyhat content, I am only delivering this information for educational purposes. I will not be held responsible for license violation. This page was copied from a google blogger page, but the user is now trying to sell this information on admin-pains.com which is why I have posted it here

The crap way

SERVER - Stop the terminal license server in services
SERVER - Go to the %systemroot%\windows\system32\lserver3. Backup both files edb.chk and TLSLic.edb in case method fails (microsoft holds licence information database in these files)
SERVER - Delete both files edb.chk and TLSLic.edb from the directory
SERVER - Run registry editor
SERVER - Go to the following key "HKEY_LOCAL_MACHINE\Software\Microsoft\MSLicensing\"
SERVER - Note there is subkey named "Parameters"
SERVER - Delete subkey (I have noticed that if I don't delete this key license server returns old database)
CLIENT - Go the client that has expired terminal evaluation period
CLIENT - Run registry editor
CLIENT - Go to the following key "HKEY_LOCAL_MACHINE\Software\Microsoft\MSLicensing\"
CLIENT - Note there are two subkeys named "Store" and "HardwareID"
CLIENT - Delete both subkeys
Do NOT connect yet to the terminal server with the client!
SERVER - Change the date on the server to lets say year 2014 (this is used to change expiration day so you don't need to repeat following steps every 90 days)
SERVER - Start the terminal licensing service
CLIENT - Connect the client to the server
CLIENT - Note that windows recreated new key in "HKEY_LOCAL_MACHINE\Software\Microsoft\MSLicensing\". This new key holds new expiration date on year what you choose to licence expire.
SERVER - Go to the Terminal server licensing in Administrative Tools
SERVER - Note that temporary licence now expires on year 2014. Issue date is also at year 2014 but information is not important for clients to function. Server just saves expiration date on client.
SERVER - Return date on server to today date
You have Terminal Licence that expires at date that is long in future :)

Note that this day hack works only when date is changed on server. It means that client will get "long" expiration date only if date on server is changed. I recommend that you change date on server and leave it for few days, or how long is needed for all clients to connect to server. When all clients connect in few days return date on server to today and all clients will have date that will expire in 10 or 15 years or whatever year you choose.

So there we have it, free terminal services (hopefully). I have not personally tested this.