I have a ceaser guerini which came fixed bottom barrel first phoned them up they sent me a different selector
Which was a five min job to change so I would say yes it can be changed were you would get one I don't know .CG sent me one for free and told me how to change it .good luck with sorting it
My Miroku was the same, take the stock off and there should be a very small pin in the receiver just under the safety catch, just tap it out with a suitable pin punch, job done.