You're absolutely right that bytecodes in general are just like any other instruction set, so can be modified etc. I guess I'm using the term 'bytecode' to ref

You're absolutely right that bytecodes in general are just like any other instruction set, so can be modified etc. I guess I'm using the term 'bytecode' to refer to systems such as Java, where they don't let you mess around with it much. It's almost always the case for any implementation of a bytecode system that they don't treat it as writeable data.