How to modify or remove the No SIM Card message on lock screen?
Since you are rooted and comfortable with custom ROMs and Xposed etc, you can use Clean Lockscreen.

If you don't want to use an Xposed module, add the following line to your build.prop file: (After you made a backup!)

ro.config.donot_nosim=true


Now reboot your device. If you still see this message change this line: 

ro.config.tima=1


To this:

#ro.config.tima=1


Then reboot your phone, and if that didn't work, change the previous line to this:

ro.config.tima=0