Given that the various Preferences are currently, and have been for quite some time, only used when initializing `PDFViewerApplication` re-loading them when a new PDF file is opened in the viewer is essentially a no-op.
Furthermore, with the only usage of `BasePreferences.reload` now gone, the value of that method seems questionable at best. In the event that the functionality is actually needed again, similar to the `ViewHistory`, it'd probably make more sense to simply replace `PDFViewerApplication.preferences` with a new `BasePreferences` instance instead (using e.g. `DefaultExternalServices.createPreferences`).