what is the general word for a "language-changing" process?

The closest I can come to a term meaning, generally, 'language-changing process', is 'diachronic process'.

An offshoot of 'philology' (see Josh's answer), the scientific study of language change over time is now called 'diachronic linguistics', or 'historical linguistics'.

'Philology', in one sense, was the term used in British English to name the scientific study of the history of language:

3. The branch of knowledge that deals with the structure, historical development, and relationships of languages or language families; the historical study of the phonology and morphology of languages; historical linguistics.

["philology, n.". OED Online. December 2015. Oxford University Press. http://www.oed.com/view/Entry/142464?redirectedFrom=philology (accessed March 08, 2016). Italic emphasis mine.]

As pointed out in a note following that OED Online definition, however, use of the term 'philology' in the given sense was never current in the U.S., and is becoming rare in British use:

This sense has never been current in the United States, and is increasingly rare in British use. Linguistics is now the more usual term for the study of the structure of language, and (often with qualifying adjective, as historical, comparative, etc.) has generally replaced philology.

(op. cit.)

Language change is variation over time in linguistic features such as phonology, morphology, semantics, syntax and etc. Such changes are the fit subject of diachronic linguistics, where 'diachronic' means

2. ... Pertaining to or designating a method of linguistic study concerned with the historical development of a language; historical, as opposed to descriptive or synchronic. ....

["diachronic, adj.". OED Online. December 2015. Oxford University Press. http://www.oed.com/view/Entry/51786?rskey=vPcXSx&result=1&isAdvanced=true (accessed March 08, 2016).]

Thus, the processes of change in language can be lumped together and called, generally, 'diachronic' processes.

Lacking further context, and because of the somewhat ill-defined reference of the "privilege" you mention without that context, I'm not sure, but I think 'diachronic' might work in your example as it stands:

Benjamin thinks it should not just be sacred texts which are given this diachronic privilege.