Assad also said there would be no negotiations with those who support outside military or political intervention, China's CCTV reported Monday.
"We will not negotiate with those who are armed. We only agree to negotiate with an opposition that conducts political activities rather than terrorism," Assad said. "No country in the world would negotiate with terrorists. Therefore, those who lay down their arms we will negotiate with."
If his conditions are met, "all things can be negotiated," Assad said.
That includes the country's charter and the presidency," Assad said.
"If the Syrian people want to change the form of government, it can be presidential, parliamentary or others," he said.
"Personally I don't have any problem. I'll agree with the wish of the Syrian people."
Syria submitted an initial declaration to the world's chemical weapons watchdog last week outlining its inventory of chemical weapons as part of a deal reached earlier this month by the United States and Russia to begin Syria's chemical disarmament. The plan calls for international inspectors in position to secure that arsenal no later than November.
The United States and other nations blame Assad's regime for an Aug. 21 chemical weapons attack outside Damascus that U.S. officials have estimated killed 1,400 people. Syria and its biggest ally, Russia, counter that they think rebels -- the regime consistently calls them "terrorists" -- used the weapons.
Assad said the weapons stockpile is secure, despite the civil war that has ravaged Syria for more than 2 1/2 years.
"Chemical weapons are safely stored to prevent terrorists or groups from other countries from taking them over," al-Assad told CCTV.
Asked if more than 1,000 tons of chemical weapons were in Syria, the president said, "Syria has been producing these weapons for decades, and it is quite natural that there are large quantities of them."
Russia accused Washington of engaging in "blackmail" that could scuttle the deal for Assad to give up his chemical arsenal.
"Our U.S. partners are beginning to blackmail us," Foreign Minister Sergei Lavrov told Russia's state-owned Channel One.
Lavrov contended Washington was threatening to sabotage all the work he and U.S. Secretary of State John Kerry put into securing Syria's chemical arms unless Russia backs a U.N. Security Council resolution that allows the use of military action if the Assad regime doesn't comply with its disarmament obligations.
U.S. negotiators "see in the Russian-U.S. agreement not a chance to save the planet from a significant quantity of chemical arms stockpiled in Syria, but an opportunity, denied them by Russia and China, to in fact carry through a use-of-force resolution aimed against the regime and sparing the opposition, to accuse Bashar Assad of everything and thus untie their hands of power scenarios," Lavrov said in Russian remarks with translation provided by the Los Angeles Times.
A senior U.S. State Department official told CNN Washington would not "litigate the details of a potential resolution in public," but said the U.S. diplomatic team at the United Nations wanted to achieve a Security Council resolution "with the strongest possible enforcement mechanism."
The official said Lavrov and Kerry spoke Sunday to reiterate "the importance of working together on implementation of their agreement in Geneva [Switzerland]."