Floating floor tile (Snapstone). Can unlevel be fixed?
I'm assuming that there's a depression or hump in the floor that you'd like to eliminate or reduce. The only right way is to disassemble the floor and prepare the subfloor properly. If you do it carefully you probably will be able to reuse the tiles. 

Problems with your ideas: 


Foam will compress and degrade over time. Also, it's extremely sticky and difficult to remove. Massive mess even if you manage to get it under the tiles.
Levelers will not "seep" through the cracks in any appreciable quantity, and certainly not enough to give your tiles the full support they require. Also, mess.
I'm not sure how this resolves the issue as I've assumed it.