On my shiny new M8, Twitter and Facebook came preinstalled as system apps.
I took the latest version of each app (from the Play Store) and pushed my own hd-ish notification pngs into each apk. Then I signed them and tried to side load them on the M8. I got the conflicting signature error message. So I tried copying the META-INF and androidmanifest from the play store version to my modded version. Nothing.
So I tried uninstalling the system versions with RootUninstaller. The apps can be frozen, but not uninstalled. If I uninstall them, they just magically reappear when I exit RootUninstaller.
I am at a loss of what to try next. I know the simplest solution would be to uninstall the system version then side load my own modded version, but it seems the M8 doesn't want to get rid of it's system version of Twitter & Facebook. I've also tried using the SE Linux Mode changer before uninstalling and no dice.