Hi Ripee and all users/readers of this blog, I did ask for some help with the Pie build but i did some digging around and also I looked at some of my older custom roms that where called official. - I made some changes to the Build.prop file and then pushed it into the build using TWRP recovery, - there are now no trust errors, no issues with my test app - stagecoach busses that was always detecting custom rom, obviously finding test-keys.
Google pay works, Bank of Scotland works and that stagecoach app.
Changes to the Build.prop are:
ro.build.display.id=rr_serranoltexx-userdebug 9 PQ3A.190605.003 eng.endre.20190616.090106 release-keys
I replaced the words test-keys with release keys
ro.build.tags=release-keys
Same again removed the words test-keys
ro.product.model=GT-I9195
I changed the model to GT-I9195 from rr_serranoltexx
I then renamed the existing Build.prop to Builds.prop - so I've got it as a back up and then copied in my new Build.prop.
Important, the phone will boot loop if the file is not changed from read-write to read-only - the way to do this in TWRP is to modify the file using file manager and selecting the file and then click chmod 755 and then just reboot.
For Google assistant/google app the fix is to boot into recovery, delete a folder found in system called velvet(don't know why this is the actual google app going by some crazy name.) , re-download google.app from playstore, boot back to recovery and copy the Google.app into system/priv-apps (note google is called Googlequicksearchbox in recovery.
after doing this I have thoroughly tested Google assistant and it is working fine.
I suspect some of these changes will work with the 10/Q build but I have not tried them because the 9 build is much more flexible and allows me to add a nav bar without disabling the hardware keys. Also the nav bar is customisable allowing me to add two extra buttons for application quick launches.