Eight women were released from prison on Monday, after the president amended the law.
Pervez Musharraf signed an amendment on Friday to the Hudood Ordinance allowing women awaiting trial on charges of adultery and other minor crimes to post bail - a right previously denied.
Officials say 1,300 women stand to be released on bail immediately as a result of the amendment.
The eight women, aged between 20 and 30, were released from Kot Lakhpat jail in Lahore, capital of the eastern Punjab province, said Sarfaraz Mufti, chief of prisons in Punjab.
The women, who worked as maids, had been held for 10 days to three months, over allegations that they stole money and jewellery from homes where they worked. They face up to seven years in jail if convicted, Mufti said.
The law also affects the way alleged female victims are treated.
Hasina and Sumera Mai, aged 16 and 14, say they were gang-raped by five men in front of their parents in eastern Pakistan seven months ago.
Unusually for a rape case in Pakistan, the sisters are fighting for justice, and have threatened to kill themselves if they fail.
"They have ruined us. They have ruined our dignity. We will not let them go," Hasina said. "We don't want anything less than death to these people."
Their stand is brave, but the law is still stacked against them.
A former military ruler, Mohammad Zia-ul-Haq, introduced the Hudood Ordinance in 1979 in a move to Islamise the legal system.
Hudood refers to punishments in the Quran for adultery and fornication, as well as for consuming alcohol, making false accusations and stealing.
Under the ordinance, a man and woman found guilty of having sex outside of marriage could be sentenced to death by stoning or 100 lashes. Drinking is punishable by 80 lashes and theft with amputation of the right hand. Women could not - until the amendment - be let out on bail.
Rights groups say the Hudood law
discriminates against women
The law makes prosecution in rape cases virtually impossible as a rape victim must produce four pious, male Muslim witnesses in court to prove the charge. If the woman fails to provide proof, she faces the charge of adultery and imprisonment - a very real possibility for Hasina and Sumera.
In practice, Islamic courts do exercise discretion over rape cases, but not often enough, according to rights activists, who say there are about 6,500 women in prison, more than 4,000 of them on Hudood violations, the Human Rights Commission of Pakistan says.
Some clerics say the law is divine.
But human rights groups have been demanding for years that the law be repealed, saying it discriminates against women and is open to abuse, even if the punishments have rarely been carried out.
They also say the ordinance is a misinterpretation of Islam.
Their arguments gathered force after Mukhtaran Mai, the victim of a tribal council-sanctioned gang rape, also in southern Punjab, four years ago, stood up against Pakistan's male establishment to become an icon for rights groups worldwide.
Shahid Shamsi, a spokesman for Jamaat-e-Islami, Pakistan's largest Islamic party, said his party was not against changing the law but did not support repealing it.
Pakistan society appears torn
over women's rights
Hina Jilani, vice-chairwoman of the Human Rights Commission of Pakistan, said: "We want that Hudood Ordinance to be repealed altogether. It cannot be reformed or amended."
The debate highlights a long drawn-out battle between conservatives and liberals over the direction of Muslim Pakistan.
The pro-reform findings of a government-appointed panel of religious scholars released this month raised hopes that Musharraf will take decisions that past Pakistani leaders have ducked for fear of upsetting an influential Islamist lobby.
"We have to remove inequality. We have to give relief and comfort to the women," Musharraf recently told rights activists, saying he would back moves to amend or repeal the laws.
Sumaira Malik, Pakistan's minister for women's affairs, said: "The government will undo all those un-Islamic and inhuman laws enacted in the name of religion."
Wasi Zafar, Pakistan's law minister, said last week that "many religious scholars have admitted that certain laws are required to be amended".
"The government will undo all those un-Islamic and inhuman laws enacted in the name of religion"
Sumaira Malik, Pakistan's minister for women's affairs
But he said the "major defect is the misuse of the law", rather than any intrinsic flaws.
Zafar said his ministry would complete a draft of amendments this month to be presented to parliament.
It is unclear, however, whether any legislative change made by the government would penetrate areas ruled by tribal councils in remote areas that remain quite independent of Islamabad.
And for all Musharraf's intent, further reforms could be hostage to the political situation, with elections due next year and the Islamist parties already drawing battle lines.
After seizing power in a coup almost seven years ago, Musharraf needed support from Islamist opposition parties to get parliament to vote him in as president in 2003.
According to Hasan Askari Rizvi, an analyst based in Lahore, "if the government comes to a conclusion that it needs support of the religious groups then this campaign will be stalled".