i'm currently working on an addon scenery for Contadora Island in Panama, and up to now, i've loved it. However, if i follow this tutorial's instructions: https://www.flightsim.com/vbfs/showt...cenery-for-FSX then it makes me delete the entire default terrain tile so i can make my own custom terrain for the island, but this means that it will delete the rest of the country! this is a big issue, so i would like to know if there's a way to delete part of the default terrain file so the default island doesn't exist and only my version of it does in fsx.

this is what it looks like if i don't load MY terrain file and leave the DEFAULT terrain file:
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the country is there, but...
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the island has a bunch of excess terrain!

this is what it looks like if i load MY terrain file and move the DEFAULT terrain file out of it's corresponding folder
Click image for larger version. 

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the whole country is missing! but...
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the island looks fine!