I am not entitled to do support for other product.
This is my method to disable UTX, open Setup Tool on Terrain tab select "Quick Ultimate Terrain Enable\Disable.
I advice to use this method to disable UTX, but if you are an expert, you can do it also in scenery library inside FSX.
You will be able to uncheck(disable temporary) all 3rd party addon.
Even FSDT airport can be unchecked.
hope this help.