From an object-oriented point of view, it seems wrong to manipulate a vessel's animation states from the outside. Only the vessel should be responsible to keep its animations in sync with its 'logical' state, so the animation IDs and pointers are protected resources inside the vessel class.
For example, your "gear down" request not only affects the animations, but also the touchdown points, surface friction coefficients, cockpit switches, etc. All this has to be taken care of by the vessel, which you would bypass if you set the animation state directly from the outside.
If I understood correctly your plant is producing vessels, so the "gear down" problem arises at the point of vessel creation. Maybe some sort of intelligent vessel constructor method would be required, that allows the vessel to set its initial state according to the general situation it is placed in (e.g. "launch-ready").