This was, in fact, more or less pioneered in languages that aren't homoiconic in the same manner as Lisp is (code that used self-modification for reasons like time or space optimization was, if not common, at least known of in the early days of electronic computers). Arguably, machine code is very much homoiconic; what is beautiful about Lisp is that the underlying structure of program/data is regular and nicely-abstracted.

I think you could solve most of the problems that you'd need this property for with closures. If the bulk of the execution is defined with them, and you have closures defining which other closures to run, you can have them swap each other out.