There is not a mechanism via Anaplan that would allow you do mask the data on the "fly" from a model. Let me ask you a couple of questions:
Why are you copying production data back to a test or dev workspace?
If you had ALM, you could test your processes and then sync to Prod (Dev->UAT or Dev->Prod)
By having ALM, you would develop the model structure in Dev and then sync the structure to Prod, thus not having to worry about the transactional data since transactional data does not get synced to Prod.
I understand your need to copy the production data into the test model. The production data can grow and change over time, people want to have a similar environment to test the production like scenarios. We can design a process (set of actions) which can rename the list members dynamically using a encrypting formula, for eg converting 'SAMPLE' to 'TBNQMF' (just the next letter of each letter, or any simple way to hide the original name), but you need to use the same code in production and test. The text encrypting operations will be costly on performance. This renaming process should be run as soon as you create a test copy.
Thanks for suggestion, the data exists in a couple of Lists & in a number of Modules, after copying the data can i run the formula on list/modules in copied model directly or should i have separate line items for modules & lists for formulas
I think just renaming the list items are sufficient, unless you want to mask the other text line items stored in the modules.
You may need few text formatted line items to encrypt the list item names using formula. No other change to existing line item formulas. Create a saved view based on this, import this saved view into the list.