Normally you would have to speak to customer care to get a downgrade license as the 2012 license will not work with 2010 R3. However because 2010 R3 is in partial support I have a feeling the issuing of 2010 R3 licenses is now not possible so if you do not already have license codes that work you may be stuck. If you already have 2010 license codes (that you got legitimately in the past) then these never expire so there is no legal issue anyway you can just use them.
If you however get 2010 license codes from an illegitimate source and own comparitive 2012 licenses that you can prove aren't being used elsewhere then it probably becomes a question for legal types so can't be answered by anyone on these forums
Why do you need to run 2010 R3? (it is in partial support so no engineering fixes, no support for new environments, no fixes for vulnerabilities etc)
