unconventional notational need

I’m using this workaround, but it does not show up in parts. Any way to get the same line in parts?

Or is it that everything I do in engrave mode on the score will not effect the appearance of the parts?

I’m afraid this is one of those things that is layout-specific.

As far as I experienced the pitch and duration of a note will be the same. Forced duration will carry over. Articulation will be the same. Dynamics, I am not sure about prefixes and suffixes. If they are in the library and are accepted by popover input, they will, if input via property panel it has to be repeated each time. Gradual dynamics: If you change the type in the score, you will have to do it again in the parts. Position: If you nudge the position of an element in the score, you will have to check the parts too. Visibility (colour opacity): same here, independent between score and parts. Same with scaling things.
As you can see, it gives a tremendous flexibility to have things independent between score and parts - but it can be quite a hassle if one just wants simple 1:1 transfer…