If you change the title of your post that is already ranking on Google, you might change the dynamics behind your high ranking.
One key dynamic of course is the title of the post.
So if you think you're going to rank higher by including the target keyword that SEMrush tells your post triggers in their analysis, you might be in for a rude shock.
I suggest that you look at the trajectory of your post.
If it continues to rise as your interlink to it and as you add content to your blog posts, you need to leave it pretty much alone.
On the other hand, if your posts rose a little bit in the rankings and then sank, that is when you can start tweaking it.
But if it's successful and it continues its upward trajectory, leave it alone.