Yes it will damage it. You can not mix dexcool with Ford antifreeze. You will need to flush out all the coolant and replace it. If you can tell me the year I can recommend the correct coolant for you.
Dexcool will gel up when mixed with other coolants.
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Your car uses Ford gold coolant. Here are the specs and the part number.
Motorcraft Premium Gold Engine Coolant VC-7-A
You can get a substitute at most parts stores just make sure to tell them your car takes gold.
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I would drain it out, fill it with water and let it warm up. Drain and repeat. Now it will be fine to fill with new coolant. When you add the new coolant add a 50/50 mix of water and coolant.