I have a trial coming up. The victim executed an affidavit of non prosecution in exchange for restitution after the defendant was indicted. I don't think evidence of the affidavit and restitution paid after the commission of the crime is admissible at the guilt/innocence phase of the trial. Does anyone else have an opinion? As always, your assistance is greatly appreciated.

Before the new Penal Code in 1994, that was called the criminal offense of "compounding." Maybe I am missing something, but now it appears to be the criminal offense of Tampering With a Witness -- PC 36.05(5). The defense set our in subsection (c) does not apply because presumably you did not participate in this agreement!

But do you really want to keep it out? The defendant tacitly admitting guilt by paying restitution?

You might also think about this like a partial settlement in a civil case, or an offer to settle. Then TRE 408 may be of some help, but only by analogy.