Can parties agree, both before and during trial, to waive, forfeit, or modify the rules of evidence that apply in trials to which they are or may become parties?

California & Hawaiian Sugar Co. v. Kansas City Terminal Warehouse Co., 602 F. Supp. 183, 188 (W.D. Mo. 1985) (holding, in plaintiff sugar company's action against defendant warehouse for fraud, negligence, and breach of contract, that evidence of settlement....Although settlement negotiations and offers are inadmissible (i) to show the validity or invalidity of a claim when validity is in dispute, (ii) to show the amount of damages when the amount is in dispute, or (iii) to impeach by showing a prior inconsistent statement or specific contradiction, settlement evidence is admissible if it is offered on the issue of costs or wen it is offered to counter a claim of undue delay.

United States v. Tail, 459 F.3d 854, 859 (8th Cir. 2006) (upholding trial court's exclusion of evidence of the victims' sexual histories because such evidence showed victims' past sexual behavior or conduct).Rape shield laws frequently make it impermissible -- sometimes in trials of civil actions as well as in criminal trials -- to introduce evidence either to show that an alleged victim of sexual wrongdoing engaged in other sexual behavior or to show the alleged victim's sexual predisposition.

Fed. R. Evid. 1001(4) ("The original is not required, and other evidence of the contents of a writing, recording, or photograph is admissible if-- ... (4) Collateral matters. The....The rule requiring the use of the original writing to prove the contents of the writing -- the best evidence rule -- is inapplicable if the writing goes to a collateral matter or if -- in other words -- the writing is not closely related to a controlling issue.