Supplying reduced current to a motor
Your motor draws 1 A at "rated load".  The stall current could be significantly more, as Brian pointed out in a comment.  As the warning you quoted says, that exceeds what a normal USB port can be counted on to supply.

When you exceed specs, there is no way to know exactly what will happen.  Desktop computers usually connect the USB power line to the internal 5 V supply with just a polyfuse in between.  If the motor trips the polyfuse, then the voltage could collapse for a while, probably resetting whatever you have connected to that power.  Other motherboards may actively shut off the power for a while.  It is unlikely that a computer is designed so that a short on a USB port can damage it, but that of course can't be ruled out.

If you want to use that motor, use a external power supply rated for the current.  Playing games trying to get away with something usually just ends up without a working result and lots of wasted time.