Yes, you can flash any custom oreo ROM from development sector and it will appear again. IMEI 0 is a bug, that came if you will flash Oreo ROM with bootloader upgrading and then back to stock 7.1.1. I'm issuing same problem now. But tell you buyee...
Only reflash stock ROM - is not enough! You will need to do all the steps that i writed. Until Oreo 8 will be realised it is only way to get correct IMEI in stock 7.1.1
My English not as good as pele's
But I want to express my gratitude to autor for Windows 7 theme too. It's the best theme i've ever seen!! Respect =)
And of cource i will use your theme in my Galaxy S when it will be done