Are there any issues with adding this item (legal or otherwise) via modification if the vendor agrees and provides schedule pricing for this item?
This response is based on the information provided. We suggest you discuss with your contracting officer and/or legal department as appropriate.
Open full Question Details
In that this is sole source, you will need to document as to the reason this is the only vendor that can provide the effort just as you did in the original requirement. You did not provide details as to how much the part is estimated to cost so I cannot point you to FAR part 6 or 13. Paperwork required would depend on the cost. Once the sole source document is approved, you could then add to your schedule as convenience.
Adding a new part to a list would not be considered within current scope. The principle is the same whether the unit price is $1 or $1B. The fact that the item was/is on the current schedule does not matter as it relates to a new effort.
FAR 6.102(d)(3) addresses multiple award schedules being considered competitive. However, your situation is "sole source".