To my knowledge, 'va t'en guerre' is used as an adjective or a noun, so no need to justify the -t here as idiomatic.
You might say a bellicose person -
C'est un vrai 'va t'en guerre' = He's a real warmonger
or of an government official -
Il est très va t'en guerre = He's very hawkish
To go back to Sarita's question -
Normally the -s of the second person will be dropped in the imperative and this is also the case for 'aller'.
Va au marché me chercher du poisson = Go to the market to fetch me some fish
But when a verb is followed by 'en' or 'y' a euphonic -s or a -t- is added in the imperative to make pronunciation possible .
If you try to say -
prend en , parle en , va y , pense y you will see what I mean.
So you have to say , for the sake of euphony ( to create a pleasing sound) :
prends-en, parles-en, vas-y, penses-y ...
However, this is not always the case -
You can say -
Va y comprendre quelque chose! = Figure that one out!
Va en parler à ta mère = Go and speak about it to your mother
It is all to do with sound...
Not easy, but good question Sarita!
