The exception is that if it is a major upgrade, such that it is effectively a new/different product.

If this is the case, you need make it clear in your introduction post, how that is the case. You should reference the previous post ("Hey HN, we posted this project here a few months ago and at that time the state of the app was ___". Since then we've added ____, changed ____ and removed ____").

If you can write an intro like that and if the community agrees it's sufficiently changed, it can have some more front page time (because the discussion can be substantially different from what it was last time).