Put these Scenery only in your World Folder, after you are done 
with making your Worldmap,  or SMBX will crash at your next Attempt
to save your Worldmap, due to a Bug in SMBX !

You also can replace the GFX located in the "scene"-Folder, that you
can find in the "graphics"-Folder of SMBX. In this Case ou should make
a safety copy of the original GFX before replacing them.