If jihad has always meant to struggle and Muslim scholars have always said this in what way did Hazrat Mirza Ghulam Ahmad carry out a reform?
The point to remember is that Hazrat Mirza Ghulam Ahmad carried out a great number of reforms and the clarification of the concept of jihad was only one of them. For example, when Hazrat Mirza sahib appeared Muslims had lost all hope and blamed Islam for their backwardness. It was Hazrat Mirza sahib great achievement that he infused in their hearts the confidence the Islam shall prevail though it will be by force its arguments and not by force of arms. So much so that Hazrat Khwaja Kamal ud Din came to the UK just after the First World War and set up a mission to propagate Islam in London. Our Sunni friends laughed at him and called him mad for dreaming that he could get the British who ruled most of the earth at the time to embrace Islam.
The question fails to distinguish between what the jihad meant and what Muslims believed it meant. Although everyone agreed that according to the Arabic lexicon jihad meant to struggle Muslims generally believed that when the Holy Quran told Muslims to engage in jihad, for example “Strive for God a true striving (jihad).” (22:78), it meant a bloody struggle. Muslims even believed that to find a non-Muslim and force him to become a Muslim was jihad!
Hazrat Mirza Ghulam Ahmad explained that it is not jihad to force people to embrace Islam because Islam says there is no compulsion in religion. He further explained that Islam allows fighting because it is not a pacifist religion but only under certain conditions. Such as if religious liberty is prohibited. He established that jihad can never be abolished because it is a duty of every Muslim but that jihad with the sword can come to an end when conditions for it do not exist. He taught that in this age to engage in jihad means to do our utmost to make ourselves into model humans and dedicate ourselves to propagation of Islam and taking man near to Allah.
It is one thing to say that it is written in books that jihad means to struggle and a different matter to create an organization which has members who give up glowing worldly careers to work for propagation of Islam. Just look at the lives of the elders of the Lahore Ahmadiyya Movement and you will see this.