Shipbucket

For some times I have think about a modified Fatahillah corvette. The modifikation is to replace the 40 mm Bofors gun with a 57mm. Would that be possible?

Almost certainly (if you do it before you lay it down) you are only doubling the weight from say 3,500kg to 7,000kg ish and you have a 1450 ton ship with a 28t main gun so will not make a huge difference.
Post build as a refit it may be harder but you might do it if you remove some top weight (dnt have any details of how much spare the ships have if any ?)(swap both guns for 2x 57mm ? or remove the SSMs)
But what does 57mm give you that's better than 40mm ? (and I don't think you will fit the full CIWS 3P ammo/fire-control on a 70s corvette)