Try going to Samsung Cloud & do a System Restore. Many Android forums post repeatedly that you should create a backup PRIOR to ANY UPDATE OR OTHER SOFTWARE CHANGE. It's a safety measure in case of a bug/glitch in the "new" programming being transferred to the device. in the case of the 9-Pie Update, for many it's the only way to get back the preferred features.
You're not suggesting that he (or anyone else) can revert to a previous version of Android by a "system restore" are you?? Cause that's never going to happen... ever. The ONLY way to revert to a previous version of Android is to use Odin & that's IF the Bootloader version hasn't changed 😉🐧 As for the OP's issue - Change the theme on your Messages app.
I hate the update! I hate the way the text messaging looks too & that I cannot change it ! As well when my phone rings I cannot answer the phone at all!
