If you just want to use a single line staff with a short barline, you can use a percussion instrument like Claves, so there’s no need to mess around with the instruments.xml file. If you want a 0-line staff, or longer barlines, or something else, then you may need to edit the instruments.xml file.
There’s no way to change an instrument definition within Dorico like there is with other notation programs. I assume at some point there will be a full-featured instrument designer but for now you are limited to the instruments already configured in the program. This can be severely limiting if you want to do something custom that the developers haven’t thought of. The workaround is to modify your instruments.xml file. In Windows this resides in Program Files/Steinberg/Dorico3.5. As this is in the Dorico system folder and not the user folder, modification of it is not officially supported. Be sure to make a backup of the original file before making any hacks.
For example, here I’ve made a modification in my instruments.xml file to an instrument I’m not likely to ever use to be a 0-line staff, as there are no instruments already defined in Dorico to be a 0-line staff:
When added to a score, your chord staff could look like this:
To remove the first rest, you need to modify it manually, after that Remove Rests will work, or you can copy the one you modified. I started by setting the rest to -1 in Properties which is a manual edit that will allow Remove Rests to work after that bar:
You can make a lot of items invisible in Dorico by setting the Alpha channel to 0 as shown below. The catch is you have to remember to export PDFs in Color mode, otherwise that channel isn’t active.
Hope that helps!