Modify the bytecode and not compiling

Making byte code manipulation to fix problems. I had to fix a problem in some code that was written 10 years ago. I was not able to modify it without needing to compile everything with ReCAF.

It made me think of stories where mainframe developers told that in the good old days. It was practice to modify the assembler code of a running program. Not really sure that was something that was governed.

Have you made such changes in running programs and why?