Just getting an unpacked version of the TERA client is fairly simple. If you run x86 Windows or are in a VM, simply follow instructions at forum.tuts4you.com/topic/34085-themida-winlicense-ultra-unpacker-14/. If the script fails with "No API found", remove both dbghelp.dll from the TERA Binaries folder and the ollydbg folder. Then it should run successfully and give you a ~37MB unpacked TERA.exe.
If you're running x64, things are a bit more complicated. Usually ScyllaHide with the Themida x86 preset should work, but I've had to install TitanHide which is fairly complicated and requires patching your kernel. So I recommend you try ScyllaHide first and ask for help with errors in this thread before installing TitanHide (I'll explain how if the issue arises).
BHS is using a 2012 Themida version (I believe 2.2.6.0 or so). Also, I noticed that after some time the game closes if ran with the unpacked exe, but due to crashdump autodeletion I haven't had the chance to check why.
While I'm writing this: does anyone have an idea why TERA.exe fails with 0xc0000005 trying to access a nullpointer only when launching in a debugger? Attaching works fine. I'm trying to set a breakpoint to find out where the keys are stored in the code, but the most I managed was pause within a decryption routine, which isn't particularly useful since the keys are transformed there. Looks like 5.6.0 or 5.6.1 Crypto++ is used for crypto.