I'd like to change permanently the value of DATEFIRST (which is used for functions like DATEPART)
If I do this :
SET DATEFIRST 1
I must say this took some research on my part. Take a look at the following query. You will notice the datefirst field. I would imagine there are all kinds of permission implications that go along with changing language settings at this level.
SELECT * FROM sys.syslanguages
I don't have a server I can test this on at the moment but I would imagine through a set statement you could set the datefirst column to whatever you wanted it to be.
TEST TEST TEST as this will have huge implications across more than problem you are trying to solve.