Sequence of the working procedure: force-stop the app, pull the prefs XML with run-as cat, edit it locally, push it back through stdin with run-as sh -c, relaunch.
Android

Seeding SharedPreferences on an Android emulator with adb run-as (and the three ways it fails)

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To screenshot a game-over screen that needs three finished rounds and a two-day streak, write the prefs XML through adb run-as — via stdin, after force-stop.