Bro there is a way to sign in into Google account in your mod Without root or patch
First install the original version and log in to you account fully . Then go to file manager >Android>data>Shadow fight 3 file and rename it by adding a letter next to it. Then delete the original app.
Install modded version . Rename that file by removing that extra letter. And open the game. Your game will keep on being updated to Google and you have your old ID.
My language might be tough but I guess you will understand my mistakes .