This is a problem, and I hope they once can fix this, but at the moment the only good way for me is to give another name or index in the TMT for the new revision: E.g. cube-v01, cube-v02, etc.
Then you can load the "cube-v02" without restarting Planco when you press the refresh button. But you will have then cube-v01 and cube-v02 in your scenery items.
As long as I'm tweaking the object I go that way, once its fine I make again a revision without the "vxx", which is then the final version. The others I delete from the sandbox and later from the planco tmt folder again once the game is stopped.
That seems to be the an appropriate way. Any better idea?
This approach at least has one advantage as you can compare the revisions ingame.
A lot of greets, Corkscrewloop[happy]