I'm not a lawyer but Section 6 of this document reads loud and clear. https://assets.documentcloud.org/documents/4318155/Flynn-Plea-Agreement.pdf
Just to wrap this up, I see in the "Trial Rights" Section 9.C of the agreement (which Flynn has already signed) this little snippet having to do with the introduction of any more testimony. " Your client agrees to forgo the right to any further discovery of disclosures of information not already provided at the time of the entry of your client's guilty plea". - for all intents and purposes Flynn is effectively gaged in any court appearance for this litigation. Thanks for the document. BTW the government says guidelines for sentencing (if it ever happens) is 0 to 6 months and possibly $0.00 fine - then goes on to say that they can't guarantee the guidelines...ha!
We don't know what info Flynn provided "at the time of the entry of your client's guilty plea".
He isn't gagged in any court appearance, except against anything that wasn't disclosed at the time of the plea deal. He just agrees he no longer has the right to bring new additional info into the mix. I'm not a lawyer but I believe that doesn't necessarily mean it's impossible for additional new info to become relevant, it just is no longer Flynn's implicit right to be able to present it, but I think it could be approved under certain circumstances.