I haven't tried this yet, but could be helpful for translations... https://www.jewishgen.org/viewmate/

(left side) the certificate of Riga consistory dated 9th of Jan 1902 #150 about renaming of my father from Alphonse to Andrey and the certificate of assignment to Riga conscription department dated 31st of August 1900 #1650

received by K. Flyaksberger 20 August 1906

(right side)

Birth and christening certificate

Konstantin Alphonsovich Flyaksberger

issued based on article 107 of (some church regulation I guess) by the Grodno Sophia Church 05 July 1886

#290 

Grodno

Lithuanian diocese

In the metric book of Grodno Sophia Church for year 1880 there is a record #66:

born 23.08, christened 07.10

Konstantin

Parents:

senior assistant in the government office, collegaiate secretary Alphonse Fedorovich Flyaksberger, lutheran faith

his wife Nadezhda Romanovna, orthdox faith

godparents:

office registrar Nikolay Romanovich Melgunov

and Olga, daughter of deceased (military rank) Ivan Fedosenko

(priest names and signatures)

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By the way in another thread where you were asking about patronymics - this confirms the name change was official and way before 1917 revolution. I would say Alphonse has joined the orthodox church, in this case they would perform orthodox christening and sometimes assign a new name to the person joining the church.

Considering he was Lutheran in 1880 and married to orthodox and registered children as orthodox (this was a requirement to allow a marriage between Lutheran and Orthodox to be registered in orthodox church) chances are very high that faith change was the reason behind the name change