Yes. You can appeal any FEMA determination on your application, including eligibility denials and denied time extensions. The first appeal goes through the recipient to the Regional Administrator; a second appeal goes through the recipient to the Assistant Administrator for Recovery at FEMA Headquarters.
A written appeal with your argument, supporting documents, amounts in dispute by issue, and the specific citations.
Cite the rules in effect for your disaster’s declaration date. Citing current policy against an older disaster weakens an otherwise good argument.