Why reactivating Yavuz in 1968 would mean building a new ship

If Turkey suddenly had unlimited money in 1968, how extensive a Yavuz reactivation and refit could it carry out?

It would not reactivate the old hull; it would build a new ship and give it the historic name.

The hypothetical removes budget as a constraint by giving Turkey a fantastical windfall. Even then, a major refit of the old battlecruiser is rejected. Turkey would build an entirely new ship and reuse the historic name. At that point, modernization has become a successor in name only.