stem length in write/engravemode

In WriteMode(FullScore) I did shorten all the stems of my Slashnoteheads, in order to get some sort of SlahNotation.
Now going to the single parts in engrave or print mode, all stems are visible again - How come and what should I do
to avoid that?

There is no link yet between Full score and parts for most of the engraving tweakings, sometimes for obvious reasons. And since Dorico is really built with the idea of NOT using workarounds, the devs are struggling not to implement those. I’m afraid you will have to cope with it.
I remember that someone, six months ago, created a script in LUA to have slashnoteheads. You might want to have a look at that solution !
[Edit] : here it is

Thanks for your quick answer!