Grant permissions to a service launched with ADB?
I believe I figured it out.
I'll use Voice Access as the example app.
adb shell am startservice com.android.cts.apps.accessibility.voiceaccess/com.google.android.apps.accessibility.voiceaccess.JustSpeakService

Next
adb shell settings put secure enabled_accessibility_services com.android.cts.apps.accessibility.voiceaccess/com.google.android.apps.accessibility.voiceaccess.JustSpeakService

Then
adb shell settings put secure accessibility_enabled 1

Then finally delete the the readout app, to avoid the accessibility features from being overwritten
adb shell pm uninstall -k --user 0 com.lge.voicecommand

I don't think there should be any errors after that, leave a comment if there are though.