Mutual fund companies stung by charges of fraud in the market-timing scandals that have engulfed the $7.5 trillion industry for the past six months are amending their legal documents to fend off future litigation.

Even as it was settling fraud charges for $250 million last Monday, FleetBoston Financial Corp.’s Columbia funds unit filed with regulators clarifications to the company’s policies on market timing. In addition to warning investors against market timing, Fleet included this disclaimer: “There is no guarantee that the Fund or its agents will be able to detect frequent trading activity or the shareholders engaged in such activity, or, if it is detected, to prevent its recurrence.”

Fleet-Columbia spokesman Charles Salmans said the new language is intended to warn fund shareholders that no amount of diligence may be able to stop market timers intent on using evasive techniques.

“This is an effort to make sure our shareholders understand the reality of the situation, and it does not reflect an effort to ease up on our dedication to detect and deter market timing,” Salmans said.

But industry critics said the new warnings seem to be an effort by companies to shield against future legal problems should investigators find more instances of market timing in their funds.

“There is no excuse for this,” said Secretary of State William F. Galvin, chief of the Massachusetts Securities Division. “It shows me they’ve learned nothing at all from their recent experience, and they’re unrepentant.”

Mutual fund companies “have a fiduciary duty to stop it once they know it’s going on,” said Mercer Bullard, a former US Securities and Exchange Commission attorney who founded the watchdog group, Fund Democracy. “That disclosure cannot insulate them from liability.”

MFS Investment Management, which settled a $350 million fraud case with regulators last month, also added disclaimers to its fund prospectuses in recent days, as did State Street Research & Management Co., whose brokerage operations paid a $1 million fine in February for failing to stop outside brokers from making excessive trades in the company’s mutual funds.