This conclusion follows from the letter of Ministry of Economic Development of Russia, which stated that the issue of changing the provision of contracts concluded before 31 of December 2013, should be resolved in accordance with the Federal Law of 21.07.2005 N 94-FL.
The law did not allow to change the provision of the contract during its execution. Through, p. 7, Art. 96 of the Federal Law of 05.04.2013 N 44-FL provides this capability (including changing the method of providing selected).