“The big banks could already do risky trading by pretending to be market making — these changes will give them more leeway to do so,” said Mayra Rodriguez Valladares, managing principal at New York-based MRV Associates, which trains bank examiners and finance executives.

Harsher capital and liquidity requirements introduced after the crisis have been even more restraining on the trading risks the big banks can take. They will continue to exert pressure even under a softer Volcker Rule, Rodriquez Valladares said.

“If they start taking more risk, capital rules should kick in and force them to have more capital backing that risk, so that’s the backup control mechanism,” she said. “We’ll see if that will work as it should.”