Replacing Mutsu after an imagined 1930 magazine explosion

If Mutsu suffered a magazine explosion in 1930, could Japan replace her with an existing battleship design?

Probably not directly; Japan would need a new design that could plausibly meet treaty limits rather than use a proposal already known to be far overweight.

An existing large Japanese battleship proposal probably could not meet the treaty tonnage limit. British and American observers already knew the design was roughly 10,000 tons overweight for that purpose. A completed ship resembling the original proposal would therefore make a nominally compliant displacement difficult to believe. Japan would need a new design if it intended to remain within the treaty restrictions. The argument distinguishes concealed excess from a breach obvious enough for other navies to challenge.