I can tell you 2 easy ways to do this.
First the really easy one and fast one.
1. Make a "Main" group, put all the events out of the Layout in this one.
2. Add another Layout + Event sheet
3. In the new Layout:
-> Create all sprites that you need in your pause menue(includes the pause button)
-> Set all objects global
4. In the Event sheet
-> On start event that creates the pause button
-> onclick event that disable your main group
-> dynamicly create the pause menue like (set position menue (layoutwidth/2 ..))
-> insert all events that you need in the pause menu
-> onclick event that reactivate you main group
5. Now you just need to insert the event sheet in every other Eventsheet there you need the menue ;)
You can also use this menu in every other project there you want ;)
"Is it possible to "save" layout A, go to a different layout, then, "load" layout A but have everything intact. But when the player enters the door "nornally" to go to another layout, then return to this layout, all objects must return to their original places." // I really dont understand what you want ^^