Is it possible to open and edit the game I made on Core with unreal engine or get an exe file?
No it is not, unfortunately. Core can only publish to the Core platform. It wouldn't be in Core's best interest to allow distribution of games in .exe format because if they allowed that the game would be obtainable directly through Epic Games Store or Steam or whatever and that cuts out the Core platform meaning that Core loses popularity from the public eye, and therefore grows more slowly and gets less players to play other core games. The benefit, though, is that people who play other core games will see your game listed among search results. 
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Sorry i agree 50 %
it depends by money but in the end if you can create a good game you will go for unreal engine..so it s a paradox.
Btw officially is not possible..however the rules of the world are the same in every epoch!