Nigerian Vice-President Atiku Abubakar will be able to stand in Saturday's presidential poll, the election commission has said.
There was violence in towns across Nigeria
"I can assure you that he will be on the ballot paper," spokesman Philip Umeadi told the BBC.
On Monday, the Supreme Court ruled that the election commission did not have the right to disqualify Mr Abubakar over corruption allegations.
Meanwhile, about 12 policeman have been killed in the northern city of Kano.
Some 300 heavily-armed members of an Islamist group, known as the Taliban, have stormed a police station.
The army has been sent in and police have evacuated the area.
Last Friday, prominent Islamic cleric Ustaz Ja'afar Adam was shot dead in the city.
There had been doubts whether the ballot papers could be changed in time for Saturday's elections.
Mr Umeadi refused to say how Mr Abubakar's name would be added to the ballot papers at such a late stage.
The BBC's Alex Last says it is possible that a sticker with Mr Abubakar's name could be added to the ballot papers.
Earlier, police announced they had banned all open-air rallies ahead of the elections, according to state radio.
The move is intended to prevent breaches of security, after at least 21 people died in clashes in last week's elections for state governor.
The other main opposition candidate Muhammadu Buhari is holding a meeting at which he hopes all opposition parties will agree to back him in the presidential contest, against the ruling party's Umaru Yar'Adua.
Mr Abubakar was a founder member of the ruling People's Democratic Party (PDP) but fell out with President Olusegun Obasanjo last year when he opposed moves to let the president seek re-election.
The PDP has won 26 of the 33 states declared so far, including most of the Niger Delta.
Opposition supporters took to the streets in parts of the country on Sunday, claiming the results had been rigged.
Tension in the northern city of Kano has reportedly eased after the candidate of Mr Buhari's All Nigeria People's Party (ANPP) was re-elected as governor.
On election day, our reporter saw men storming a polling station and leaving with ballot papers in the southern city of Port Harcourt.
He says politicians often hire and arm young men to help them rig elections, attack rivals, steal ballot boxes and intimidate election officials or voters.
Political office is often seen as the quick path to real enrichment - a chance to tap into the country's huge oil revenues, especially in the oil-rich south of the country, our correspondent says.
Nigeria is Africa's biggest oil producer but unrest in the oil-producing Niger Delta has cut output by some 20%.
Winning from prison
The ANPP has also won the northern states of Bauchi, Borno, Yobe and Zamfara.
Mr Abubakar's Action Congress has retained control of the state of Lagos, the commercial capital and the small Progressive People's Alliance (PPA) has won in the south-eastern Abia State.
Victorious PPA candidate Theodore Orji is in prison on corruption charges.
Two other south-eastern states - Imo and Enugu - will have to re-run their elections because of irregularities, Inec says.
Results are still awaited from Taraba State.
Mr Obasanjo said on state television that Saturday's vote had "gone on very well across the country."
The presidential contest should see the first time one civilian administration hands power to another since Nigeria's independence from Britain in 1960.
President Obasanjo is standing down after two terms in office.