This response is based on the information provided. We suggest you discuss with your contracting team, program manager and/or legal department as appropriate.
Your question gives no context, so we can only answer the generic question. You do not say, but we are assuming the question relates to coding in FPDS. The answer is no. If your acquisition situation lends itself to negotiating an estimated cost, a contract type other than FFP would be applicable. Research FAR part 16, as well as the DFARS and AFFARS supplements to understand the different contract types, when they are applicable, and what limitations each has.