OK, just wondering. We used the A277 and Z240 MH (not Z240) designations as a tool for restricting single-unit old-style "trailers" from a municipality's zones (except for a trailer park) while allowing modern minihomes in residential areas (with permanent foundation requirements in the zoning by-law IIRC.)
So the handy-dandy A 1.1.1.1 says we can treat relocated buildings as existing, as long as there's some rational approach to figuring out if an existing building meets wind/snow and seismic loads in its new location.
We have a bit of a similar situation here with existing modular units from out-of-area as our jurisdiction includes some areas where the Sa (0.2) exceeds 0.7g. We haven't had to deal with units from outside that area being moved in (yet), but .... but.
We've been informed by one manufacturer of single-unit modular homes that they use longer nails in exterior sheathing in any event as part of the deformation resistance in Z240 10.1, which is handy. As for others, the difference between a seismic-suitable nail (2.5") and a standard sheathing nail (2.375") isn't much, it wouldn't be *much* of a risk, but....but.
Might I suggest a policy that evaluates each pre-constructed building on a case-by-case basis, reserving the path to an engineering oversight for structures that are of a certain vintage and/or come from climactic zones that were less onerous (ie: lesser wind/snow loads)? You might also be able to subsume an approach to moving existing non-conforming buildings (like, say, that 1920-era timber-frame church being moved into the community to be renovated into ... whatever.