Changing a program while it is running

If you use some Satori-Level language, can you change the program while it is running -- replacing functions and such?

>>1
Take a look at the kernel functions in windows, or pretty much anything from MS (incl. DX), they all have a prologue which looks like:

mov edi, edi
which is basically a 5-byte NOP. The reason? So they can place an unconditional jmp instructions (which is 5 bytes) to fixed functions, effectively producing hot-fixes, without having to reload the module. Pretty neat if you ask me.