It would be helpful if there was a way to set the style for the ties in tremolos in engraving settings.
For example in this situation I would like to have the ties show as dashed. I could go through my project and manually change every one of these ties to dashed (or remove them altogether) but I’d be happy if Dorico could do it for me 
I would vote in favor of this, but unfortunately there’s a semantic problem with the idea.
Slashes could mean “unmeasured” (a true tremolo), or a measured division (32nds, in your example), and by themselves they do not specify which. If unmeasured, then of course dashed ties are appropriate. Perhaps it was yesterday’s discussion of issues with the latter that inspired you to create this thread.
I don’t see a way to handle this ambiguity automatically, unless they give Dorico a way to distinguish the different types. As things stand, playback is always measured, while I’d guess a majority of the time the intention for most instruments is unmeasured.
Playback doesn’t have to be always measured; you can change the minimum number of slashes Dorico will consider as unmeasured in Playback Options.
