I've done a few myself and must have got lucky.
I simply scribed a lineup mark on the shaft/end and cut through the weld with a cut off tool.
I then cut the driveshaft the desired amount. On the last shaft that I cut I also had to relocate the attached weight.
I grinded down the weld smooth with a standard 4.5" hand held grinder.

Is it precise? No.
Is it perfectly balanced? No.
Can I feel any vibrations or any other adverse effects? No.
Does it work for me? Yes.

This is my personal experience and opinion. Take it for what it;s worth. It plus $1.10 will get you a cup of coffee.