If you put the stock cover back on until you can get the cable, there isn't an issue. You will be wasting some gear oil though when you change the covers. Unless you are re-gearing at the same time, in which case you have to change the gear oil after 500 miles anyway.
If you are not going to re-gear and don't want to waste the gear oil then find something that will plug the cable hole in the OX cover until you get the cable. A short bolt with the correct thread would work.
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