How do you create a schematic with modded blocks?

Yeah, you can do that. First, export a version of your mod with all of the blocks you will need in it. Put it into your Minecraft mods folder, then create a new world and build your structure. Open MCEdit and go to that world. The blocks will show as errored (purple/black squares) in MCEdit but when you put the structure in the mod it will look fine. From there, export your schematic from MCEdit and put it into MCreator. Voila!

Hope that helps,

-A

when I try to load modded blocks it just loads them as grass blocks

is there any way to do this without mcreator

Whats about the Schematica Mod?