Follows from explanations of the Ministry of Economic Development that it is possible to correct only amount, the price of goods, works, services or terms of a contract. Earlier department stated "the similar point of view".
In the Law N 223-FL it is told about an opportunity to change only amount, the price and terms. The customer shall place data on such changes in a unified information system.
The law N 223-FL doesn't allow, but also doesn't prohibit to adjust other conditions. Despite it, change of the subject of the agreement can lead to violation of the principles of this Law and purchase bypassing its provisions. In that case the court probably recognizes the transaction on change of the subject of the agreement invalid.
We recommend to customers to adhere to a line item of the Ministry of Economic Development and not to change the subject of the agreement. If it is necessary, it is better to carry out separate purchase.
Document: Letter of the Ministry of Economic Development of the Russian Federation of 25.07.2016 N OG-D28-8965