I hadn't heard of javosize before, looks interesting, thanks. Being able to update code and data on a live system is very useful and I haven't seen that for the JVM before (BEAM of course handles that :) ).
Well, there are a lot of JVM tools to inject code into a running application. Take a look at Byteman (which is much more mature than javosize, but mostly targets injecting traces for live debugging purposes)
