Looks good! Thanks for doing this. We probably need to consider improving the edit experience for the task as well (it forces you to re-enter the password every time you make a change), but this change is still an improvement on its own.
Yeah, the check-box "overwrite password" could do the trick here, and probably there is already existing code for some other Bamboo task that stores password in configuration. Anyway, I won't undertake the task of improving the edit experience of the bamboo-continuous-plugin-deployment - I assume that's OK? :)