Create a mis file with just that in it, and always start your map from that mis file is how I would do it. I don't think you can copy from one mis to another via the med. At least, not from what I can remember.
But you could always try it. Just open both maps, select all the items in your one map, press CTRL-C and then CTRL-V into the other map.
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04' Dodge SRT-4, Mopar Stage 3, 406whp/436wtq
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