Adding the clause 52.217-8 with a bi-lateral contract modification is one thing but since the option was not part of the original contract it becomes a scope issue as to whether this additional work to be performed under the option was contemplated as part of the original scope of the contract. Adding the clause is not a way to get around the requirement for competition or the need to do a J&A and in fact if the option effort contemplated under 52.217-8 was not previously evaluated as part of the initial award then a J&A must be prepared and it must be synopsized as a Notice of Intent to Exercise FAR 52.217-8 Option to Extend Services.
There is certainly sufficient case law to substantiate the opinion above for example Laidlaw Envtl. Servs. (GS), Inc.; International Tech. Corp.--Claim for Costs, B-249452, B-250377.2, Nov. 23, 1992. Wherein the decision determined that the option to extend the contract under FAR clause 52.217-8 was not evaluated as part of the initial competition, so that the exercise of the option amounted to a contract extension beyond the scope of the contract, and therefore effectively constituted a new procurement.,
You should be able to find numerous examples of this type of synopsis on the FedBizOpps website.