Hi, I just bought Mount & blade warband.
I am interested to play some mods Gekokujo & Diplomacy 42+POBD
But it seems they require older version

The game that I bought, when I installed without any patch
it already display version 1.162
So..... I download patch 1.158 from gamefront
But, when I try to run it, it display error message "Mount & Blade warband isn't installed in this computer"
Which is very odd.

I did installed and it is running.
Is it possible to downgrade?
or do gog have older version installer ver 1.000 would be good.
but I suspect I will encounter another problem since
the 1.158 patch from game front, seems can't find mount & blade warband in my computer.

EDIT: grammar fix

Try contacting support, they might be able to help you with this - http://www.gog.com/support/contact

Thanks for the suggestion.
I'll go ask support.

GOG usually offers the latest official version available, so I'd be surprised to see an older version here. As for downgrading, that seldom works, because at the time the patch was released, the newer version wasn't, so downgrading only works by sheer luck. If the patch is simply a collection of files that are replaced, but it doesn't start as a newer or no version of the game is detected, you could try to extract the patches content manually e.g. with 7zip. There's a small chance, that it works. If the patch alters the game's executable, which I don't know, you're out of luck. I'm 100% sure the older patch isn't able to edit a newer executable.

As far as I know newer versions of WB rarely cause issues with mods designed for earlier builds (if any), I do it all the time, specially with mods already completed like Brytenwalda.

Just download Gekokujo and give it a go.