Only one of the OP’s objects, the tremolo, can be set to a shortcut (without perhaps some major JSON editing).
Currently, key signatures, time signatures, and tempo have a separate section in their panel for “Used in this flow.” I imagine that, given how overwhelming in amount dynamics, playing techniques, and ornaments might be in a given flow, the original choice to not include such a section for these is not unusual. However, when I think myself of how often Massenet has used “pp bien chanté et dehors” in the opera I’m working on, I can see the use of a “Used in this flow” section for all of those. As long as the subpanel can still be hidden when it gets to an overwhelming amount.
But, in short, no, there’s currently no such functionality for those kinds of objects. In Key Commands you can set a two-, three-, or four-slash tremolo to a key command, but nothing there’s nothing else you can do to customize something for a more visual approach.