Testing Key Field Change in Sandbox

I'm administrating a large app involving multiple tables. An issue has recently arisen where one of our key fields in our main customer field can no longer be used as a unique identifier. This is because of expansion of our database to include customers from different regions. These customer ids can now be identical though from different regions. My fix is to concatenate the region and customer id fields and then set that as the new key field. I am cautious about implementing this change until I can test the downstream effects on all other tables. I tried to set up a sandbox so I could test the change but it does not allow me to change key fields in sandbox. Is this normal behavior? Or is there some way to test the changing of key fields without copying the whole app?

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Cadmus Kyrala
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