C3D Add labels
You can set your angle constraints to zero (0) and the landing will be in line with your original angle.
You can edit the label style and set the rotation angle...but that will change the angle of ALL the labels being used by the particular label style. So instead of that, you could copy the label style, assign the copy to that single label you want to align and edit THAT rotation angle...or just explode the thing into MTEXT and say forget it (as I do). Would love to hear if anybody here knows a practical method, that’s all I have figured out.
If you using MLeader just rotate it all and move arrow grip to needed location (original position). It working perfect after that.
I'm going to disagree with all of the above. Since the title of your post is C3D Add Labels I'm assuming that you are using a C3D label and not a multileader (which is exactly the way you should do it). There are angle constraints within multileaders, but not within a C3D label. You can only set a rotation angle for the label itself. I always advise against exploding anything C3D.
So here's the good and bad news. The good news is that you should be able to get your text to rotate to be aligned with your line by setting, within the Dragged State tab, your Dragged State Component Display to As Composed. Be advised that this will impact all your other labels, so I would advise copying your original label style to create a new one. The bearing should now be aligned with your line, however you want it to actually be perpendicular, so you will need to set your rotation angle to either 90 or -90 degrees.
Now the bad news. That doggone tail is not going to rotate with your label. Autodesk has not made it possible to do that. You will end up with something like I show attached (which has the rotation angle set to be perpendicular). Your options will either be to toggle off your tail, which will leave the arrow and first segment, or to not have a leader at all. You can then add a tail or a qleader manually to get what you're looking for. I'm working in C3D 2019 so this has been a known problem forever.