In the PCB window, I’d like to have component values rather than references on my silkscreen and have those under the component rather than next to it.
I’ve found how to do this one component at a time, but can’t find how to do it with a bulk selection (or how to set it as default).
Use Edit–>Edit Text&Graphics properties.
Set scope to affect only Values.
You could also try to utilize the appearance panel + selection filter + display mode (dim/hide) so you are able to select only the FAB values. Then use the left side properties panel to change size/layer for the values.
The “defaults” for these are part of the footprint libraries. Each footprint has default locations and layers for it’s own texts. KiCad’s own libraries are read-only (and for good reasons), but you can copy symbols and footprints to your own personalized libraries, and then modify the default layers and locations of all texts and other things. And with this approach, the footprints at least a lot closer to how you want them for the next project in which you use them.