This is a commonly performed task, and it's easy to do. You'll need an external hard drive, and image backup software. It won't take long. I'll outline the procedure below. There is one 'trick' that you must know.
Step #1: Make an image backup of the 256 GB drive, with image backup software. Store the backup on the external hard drive.
Step #2: Make an image backup of the 1 TB hard drive, with image backup software. Store the backup on the external hard drive.
Step #3: Restore the backup of the 250 GB hard drive to the 1 TB hard drive; and restore the backup of the 1 TB hard drive to the 250 GB hard drive. Each hard drive now contains exactly what the other hard drive previously contained.
Step #4: Power off the computer - remove the power plug from the wall socket - and open the computer's case.
Step #5: This is the 'trick.' A computer boots from the first hard drive that has a bootable operating system. The EFI (or the BIOS, in an older computer) checks the first hard drive in the computer for the presence of a bootable operating system. If it finds a bootable operating system in the first hard drive, it transfers control to that operating system. If it doesn't find a bootable operating system in the first hard drive, it checks the next hard drive, and so on, until it finds a bootable operating system.
Since Windows is now installed on the 1 TB hard drive, you want the EFI (or BIOS) to check that hard drive first. To do that, switch the data cable from the 250 GB hard drive to the 1 TB hard drive, and vice versa. I'll explain why this works:
Presently, the data cable for your 250 GB hard drive is plugged into drive connector '0' on your motherboard, and the data cable for your 1 TB hard drive is plugged into drive connector '1' on your motherboard. The EFI (or BIOS) is going to check whatever hard drive is plugged into drive connector '0' first, for the presence of a bootable operating system. When you switch the data cables, the hard drive connected to connector '0' is now the 1 TB hard drive ... the hard drive that has Windows.
Step #6: Close the computer's case, insert the power plug back into the wall socket, and power up your computer as you normally would. Success!
Essentially, nothing has changed. You simply moved your wallet from your left pocket to your right pocket, and your keys from your right pocket to your left pocket. Everything is still in the same pair of pants (or skirt, as the case may be.) For that reason, there are no problems with licensing or activation for Windows and your other software.