"Muḥammad" can be a a qualifier for anyone : Abraham, Moses, Jesus, Hud, Salih, etc.
“muḥammad rasūl Allāh” >>>“praised be the Messenger of God.” That such a meaning is in accordance with Arabic grammar can be seen when we take the well-known phrase from Christian liturgy (Mt 23:39): mubārakun al-ʾātī bi-smi-al-rabb (“benedictus qui venit in nomine domine,” Blessed is he that cometh in the name of the Lord”). Mubārak (“the blessed one”) and muḥammad (“the praised one”) can be considered synonyms, but also the second part of the sentence, “he that cometh in the name of the Lord” is next to synonymous to “he is the Messenger of God,” which would make the second part of the shahāda a quotation from the Bible.
Yes, it is scientifically plausible. Manfred Kropp arrives to the same conclusion without the use of the shahada and in taking another example : the inscription of the Dome of the Rock :
(
S)bi-smi llaahi r-raHmaani r-raHiimi laa ilaaha ill.aa llaahu waHda-huu
laa shariika la-huu la-huu l-mulku wa-la-huu 1-Hamdu yuHyii wa-yumiitu wa-huwa calaa kulli shaycin qadiir. MuHammadun cabdu llaahi wa-rasuulu-huu
MuHammadun cabdu llaahi wa-rasuulu-huu : can be scientifically translated as :
Praised be the servant of Allah and his apostle
Which person is it?
(SE)cinna llaaha wa-malaacikatu-huu yuSalluuna calaa n-nabiiyi.
yaa-ayyu-haa lladhiina caamanuu Salluu calay-hi i wa-sallimuu tasliimaa Sallaa llaahu calay-hii
wa-s-salaamun calay-hii wa-raHmatu Uaahi.
yaa-ahla 1-kitaabi laa taGluu fii diini-kum. Allah and his angels pray on the prophet
(remark the use of nabi and not rasul...)
Which person is it?
Does the rest of the text identify him?
yaa-ahla 1-kitaabi laa taGluu fii diini-kum
This phrase show that the text is dealing with Christian thing and not ("muslim")
It's Jesus the text is talking about since the beginning but "Jesus" according to the Quranic idea : rasul/prophet who is seen erroneously by the Christian theology :
yaa-ahla 1-kitaabi laa taGluu fii diini-kum
as an exaggeration by the Quranic theology.
The rest of the text confirms this comprehension :
(E)wa-laa taquuluu Calaa llaahi illaa 1-Haqqa!
cinna-maa 1-masiiHu Ciisaa bnu Maryama rasuulu llaahi wa-kalimatu-huu calqaa-haa cilaa Ma1yama wa-muHun min-huu. Say nothing about Allah but the truth! The Messiah, Jesus son of Mary, is only the Apostle of Allah.
It's about Jesus and no one else.
Then it is perfectly (and reasonably) plausible that "MuHammadun" in this inscription qualifies Jesus. Kropp here his demonstration being scientifically exact, logically (like 1+1=2) he says that "MuHammadun"qualifies Jesus.
So "MuHammadun" may be not a proper name. It is totally clear to me and scientifically, regarding the Kropp demonstration, irrefutable."MuHammadun" is a qualifier, not a proper name.