Can I flash a rom, that is not exactly made for my phone, but has the some socket (MT6753)? My phone is an Elephone P6000 Pro with Android 5.1 and I want to flash the Vernee Thor's 7.1 rom. Both of the phone has MT6753. Is it possible?
Very bad idea.

They may use the same processor but other things you don't know about yet, are different. If the code isn't optimized for it, you are very likely to run into problems