There's no way you can resize a level to the left. But try this:
Resize the level to how much you want added onto the left
Then select EVERYTHING by holding right click
And try and place it on the right (mouse has to be top-left corner of where you want it)
Then erase the leftover stuff on the left.
Sounds hard, but it should work if you do it correctly.
There is a way to copy a sector from a level to another level; but I've tried to do it before... and it didn't really work. But that was because of the mistakes I had made.
So just open the level through that directory in the AppData in my previous message, but not with supertux. With a normal text writer like Notepad. Then find the part where it defines the sector you want.
Here it is for me. Now just copy it all the way down...
And you will see a few rounded brackets. Select all of them EXCEPT the last one!
- AAK.PNG (2.53 KiB) Viewed 13373 times
Then now you can simply copy it into another level. (Note: In my case, the sector I'm copying is called "main." Because there already is a sector called main in this level, I'll have to rename it to something else.
- AAM.PNG (6.91 KiB) Viewed 13373 times
I've pasted our sector right after the second-to-last round bracket so the game won't crash.
Now save the file, and open SuperTux.
The sector should appear!