For SmartAss'd targets, I usually use a loader. You can use a loader to modify the method while it's in memory. Just use CFF Explorer to get the Virtual Offset of the opcode that you want to patch, and patch it in memory. If you don't want to make your own loader you can use DUP to create one for you.
Modifying the method in memory bypasses all of those checks that SmartAssembly makes to the methods/exe.