I have to extend an existing module of a project. I don't like the way it has been done (lots of anti-pattern involved, like copy/pasted code). I don't want to perform a complete refactor.

Should I:

• create new methods using existing convention, even if I feel it wrong, to avoid confusion for the next maintainer and being consistent with the code base?

or

• try to use what I feel better even if it is introducing another pattern in the code ?

Precison edited after first answers:

The existing code is not a mess. It is easy to follow and understand. BUT it is introducing lots of boilerplate code that can be avoided with good design (resulting code might become harder to follow then). In my current case it's a good old JDBC (spring template inboard) DAO module, but I have already encounter this dilemma and I'm seeking for other dev feedback.

I don't want to refactor because I don't have time. And even with time it will be hard to justify that a whole perfectly working module needs refactoring. Refactoring cost will be heavier than its benefits. Remember: code is not messy or over-complex. I can not extract few methods there and introduce an abstract class here. It is more a flaw in the design (result of extreme 'Keep It Stupid Simple' I think)

So the question can also be asked like that:
You, as developer, do you prefer to maintain easy stupid boring code OR to have some helpers that will do the stupid boring code at your place ?

Downside of the last possibility being that you'll have to learn some stuff and maybe you will have to maintain the easy stupid boring code too until a full refactoring is done)