No. According to the Financial Industry Regulatory Authority
(FINRA), (formerly the National Association of Securities Dealers), you can convert your Series 7
license into a Series 6
license if your registration is still active. If at a later time you would again like to be registered with a Series 7 license, all you need is your firm's permission. You cannot convert from a Series 7 to a 6 license and vice versa if you have not been registered with a member firm for more than two years. In this case you would need to rewrite your Series 7 examination to re-qualify as a general securities registered representative.
To read more about the Series 7, see Solving Mixed Options Problems On The Series 7