Eye can multiple corneal transplants in the same eye cause diminished vision? can excessive movement after a corneal trnsplant cause it to slip?

Possibly: Transplants are usually done for a corneal problem which threatens vision. If you have needed multiple ones, then there is probably some inflammatory or immune underpinning which can also diminish the vision. The transplanted cornea is stable as long as the sutures are in place. After removal, the new cornea is a little fragile, so you should avoid direct hits, but eye movement is ok.

Cornea transplants: Having numerous corneal transplants does not in itself cause the vision to diminish but the risk of rejection/failure increases with increasing number of surgeries and other issues (such as glaucoma, retinal issues) become more common. Once healed, normal activities can be resumed without an issue and should not cause any "slipping.".