In general, no, “in game” is supposed to just be playback. You’re supposed to actually “build the stage” in the editor. If you need additional tools to place the objects in the editor, you can build editor actors and editor widgets to help improve the editor.
One thing you could do is implement savegame for your game. This will let you re-load whatever work you did, when you re-play the game, so you can get back to where you were.
It may be possible to write an editor widget or utility of some sort that lets you load a savegame file into the editor world. I have never tried it, and chances are it won’t “just work” because of various editor-only modes and flags, but it might be worth a try at least.