Correct me if I remember wrong, but didn't we discuss this earlier and I remember it as that all space on Naval vessels are meticulously planned for and if a space isn't reserved for e.g. VLS. then finding additional space would be more difficult.
Their is VLS and then there is "VLS". MICA, Albatros, CAMM/ER, ESSM are rather short missiles that does not require strike length (7.7+meters) modules for installation. These missiles, except ESSM, are usually preferred in their own canister-launchers. ESSM is more favored in quad-packed form within normal VLS.
If referring to strike length modules then you are right, it is not feasible or even doable in some cases if not sufficient space has spared or deck plans - structural plans prepared accordingly. But for self-defense / point defense systems the installation is rather easy. You might also remember MK56 launcher for ESSM that can be installed above the deck.
And Ada-Class was easily adapted for MICA launchers for Ukrainian Ada Class project. I would say even deck plans were effected little to none during production. I would say someone has considered a certain modification for Ada-Class during 2000s when the design is created and spared certain locations, maybe not VLS but some other equipment in mind, but those spots and spaces can be repurposed for different needs. I would say Ada-Class is quite flexible except its propulsion where they focused on space efficiency rather than flexibility for that part.
