Hello, yes easy thing to do. You just need to split the mui38usr.lha into two pieces, and copy them over that way, then joing them together again once both the files are on your A3000. You can use the workbench command "Join" to join them together again, but I've had a quick look on aminet and there's plenty of programs that both split and join files such as this one:
http://aminet.net/package/util/wb/ISplitnJoinI haven't tried it, but Im sure it'll work. If not, try some of the others. Just search for "split" on aminet.
