What is the purpose of this? This seems like a very rudimentary method for scrambling your data slightly. Maybe if you could explain what the ultimate goal is we can help you find a far less convoluted way of doing it.
Given what you have posted you will have to examine sys.columns to determine the datatype of each update. This is going to be a lot of work and dynamic sql to even get close. You only mention string and number datatypes. What about dates or other various datatypes? Do you simply skip those?
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