yep that sounds exactly right

side marker ground is wire tapped to front blinkers hot...
then the side marker and the front blinker will now share a ground... which is what makes the side marker blink instead of being always on...
yeah i was confused at first too... worst case is your side marker doesnt come on at all... cause you are not cuting the wire to the front blinker...
use wire taps and it will be a simple mod, and of course cover the now unused side marker ground.