[Help]Apply UPK in the source

guys I have question I don’t know if you can help me with it

but I want to replace the ability of unreal engine 4 to create and open maps files to the old version of unreal engine 3
in this case PAK > upk. map > umap

please tell me I can do this , this the only reason I want use UDK but he have limit for using as mmorpg

That’s not possible, the file formats are very different now. Of course, the source is available so you could do pretty much whatever you needed to, but that depends on your ability.