Changing the angleI think it's important to definitely switch angles on different muscles
I'm both for and against it. You MUST have the genetics to respond well
For: If you do and again using chest as an example then changing an angle to emphasize different parts of the chest will work well. Take the Arnold era chest which was bottom heavy (see his side chest by way of an illustration) vs the 90's on wards which has a far more even top to bottom development (see Phil Heath). Some of that is different era different athletes and different judging criteria and, arguably, changing angles changing a muscles shape
Also just sheer varying the movement stops tedium and not wanting to train. You could do 4 months top, 4 middle and 4 bottom.
Against: little to no evidence of actual muscle shaping. If you are blessed (or cursed depending on what you wanted) with short insertions so have a full long bicep but lack a peak you can TRY to do what amounts to peaking type movements (concentration curls being one). You can work the inner and outer head and so on. But pretty much every single top pro ever (and a few that aren't top Olympia level) look like bigger fuller versions of when they started. Dexter Jackson is a MrOlympia and a good example.
If it worked as well as we'd like it to you wouldn't recognize even top athletes with the best genes ever cos they'd be transformed.
By all means change training to keep the muscle stimulated and, again, by all means, enjoy feeling that burn and pump in a new place. Finally maximize da f**k out of what you do have.