Hi there. Welcome to the forum.
Normally to fit bar ends, you do have to move the gearshifters, the brake levers and the bar grips in by about an inch or so. The first two just require their pinch bolt to be slackened and then the grips will sometimes just slide across and sometimes they need a bit of 'lube' before they can be coaxed in to move along.
Cheap hairspray is the best thing to use. Pry the grip away from the bars a little with a blunt screwdriver and squirt the hair spray under. It not only slides easily, but quickly evaporates to help fix the grip in place. Another application of the spray will just as easily get it unstuck again at anytime in the future.
The plug in the end of the bars will usually stay in place and the bar ends can be fitted over the top and angled to suit your needs.
Make sure everything is tightened back up.