European Muslims fought to keep the adhān in the late Middle Ages, even to the extent of changing the call. Some changes were major, some were minor, and some were a matter of life or death.
The adhān was a major point of contention as Iberian Christians invaded and conquered more and more of al-Andalus in the late Middle Ages. Muslim communities negotiated hard to maintain as much of the call to prayer as Christians governments would allow.
But while Christian sources often express much anger and fear over one specific line in particular--"I bear witness that Muhammad is the Messenger of God"--this is in the context of restrictions on the adhān overall. Laws permitting the other lines of the call while excluding that one don't seem to follow.
In fact, actual differences in the wording were present but don't seem to have been important. Remie Constable, who wrote probably one of the most important on the matter of ritualized religious noise in the Middle Ages, just notes, "The language of the medieval mosque call was transcribed in a Catalan summary of Muslim law, probably dating to the late fourteenth century, and it differs little from modern versions" (understanding that we are dealing with a third-hand account here) and "there could be variations on the muezzin’s text, the basic words of the adhān begin by praising God and naming Muhammad as the Prophet of God."
Instead, the differences in the call to prayer in Christian-ruled areas transcended words.
Sometimes it was banned altogether--including with the penalty of death. James II in Valencia in the early 14th century laid this down, and it definitely did not work out in practice the way he/the bishop he was trying to placate had intended. It also did not work out for Martin of Aragon in 1403, whose nephew promptly overturned it. This leniency did not work out for Ferdinand I when Alfonso V overturned that...which did not work out so well for Alfonso when John II allowed it again. Words and all.
That last ruling was significant.
Where an adhān in some form was still permitted, the most prominent change was the requirement to substitute music for words--usually horns; sometimes horns and drums. (This is mirrored by Christians in some Muslim-ruled areas, like Tunis, being permitted to ring their own churchs' bells). A change like this one really does drive home that some Christians feared the loud ring of Muhammad's name more than a widespread reminder of Muslims' presence and piety.
The other major strike against the ritual was to forbid muezzins from calling others to prayer from a minnaret or other tower. They might be limited to within the door [frame] of the mosque, or simply "in a low voice and in a low place," like the Muslims of Jativa in 1357.
It was not exactly fun to be a Muslim in Christian-controlled Iberia, especially towards the end of the Middle Ages (a.k.a. closer to the time they would be exiled from their homes altogether, and permanently). But Muslims negotiated hard to maintain their most important religious practices, including ones that necessarily intruded on Christian life. Not always, but sometimes, they did win--but often only with significant changes to the ritual overall.
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Further Reading:
The basis for this change itself is in a historical precedent that reaching back to even the Prophet's time.
Recorded in Sahih Bukhari, which is held as the most authentic collection of Prophetic Traditions in Islam for over a millennia, we have 2 separate instances of a Mu'adhdin (The one who gives the call to prayer) soon after the passing of The Prophet each of which call back to this being an accepted practice by the Prophet in times of extreme need, though each of those instances themselves were in relation to extreme weather.
Translated from Sahih Bukhari, Book of Adhan
Volume 1, Book 11, Number 590:
Narrated 'Abdullah bin Al-Harith:Once on a rainy muddy day, Ibn 'Abbas delivered a sermon in our presence and when the Mu'adhdhin pronounced the Adhan and said, "Haiya ala-s-sala(t) (come for the prayer)" Ibn 'Abbas ordered him to say 'Pray at your homes.' The people began to look at each other (surprisingly). Ibn 'Abbas said. "It was done by one who was much better than I (i.e. the Prophet or his Mu'adhdhin), and it is a license.'
Volume 1, Book 11, Number 605:
Narrated Nafi:Once in a cold night, Ibn 'Umar pronounced the Adhan for the prayer at ,Dajnan (the name of a mountain) and then said, "Pray at your homes", and informed us that Allah's Apostle used to tell the Mu'adhdin to pronounce Adhan and say, "Pray at your homes" at the end of the Adhan on a rainy or a very cold night during the journey."
Any report collected in Sahih Bukhari hardly needed additional verification due to how stringent the conditions were to even be included in the collection in the first place, but these reporters and the people they were reporting on were all considered Scholars of that first Generation, with 'Ibn Umar being most well known for going to great lengths that were unmatched by any other from that generation or since, to live by the Prophetic Traditions.
For a report to be included in Sahih Bukhari it had to be proven that the saying or reported action of the Prophet met with certain criteria such as there being an unbroken and known chain of narrators reaching back to that First Generation of Islam, that all narrators in that chain could have feasibly met with the one they were reporting from, that all of them had good reputations within their communities, that none of them were known to have weak memories, etc. The list of conditions is long and each report had to fulfill each and every condition to be included. There are other collections of authentic reports with less stringent conditions, but there is little debate regarding the contents of this collection.
This and a few commands from the Quran make the basis for the decision itself. Unfortunately I can not now call upon other instances where specifically the Adhan was changed in the years of the various Islamic Empires after the time of the Khulufa ur-Rashidoon (The first four Caliphs) as my study generally focused on Fiqh (Rulings about general life in Islam) and their Basis in Prophetic Tradition, my knowledge of historical events past that time period is still unfortunately limited to general overviews.
The change to command the people to pray at home is either given at the end of the call or in place of the command to come to prayer. The latter is what you hear in the somewhat viral video of the call to prayer in Kuwait as after announcing to the people to stay at home they close out with the last part of the call (Allahu Akbar/Allahu Akbar La ilaha illa Allah).
If you are interested in other affects of Covid-19 on Muslim Rituals, The Jummah Prayer (Congregational Friday Prayer) has been cancelled indefinitely in many places worldwide (The decision for this has its own basis in Islamic Tradition). There is also uncertainty regarding whether or not the annual Hajj Pilgrimage will be canceled or not this year. It would occur right at the end of July this year if it goes on as planned. If it is cancelled it will be added to the nearly 40 entries long list of instances in the last 1400+ years where it has been cancelled. Currently the Saudi Government has only asked the Muslim world to not make any plans yet for it, but have not outright cancelled it just yet.