Well I had a look at pkgmanager...

And I think the feature I was trying to get working on my pkgsrc is this one : 
- Full binary package backup support to facilitate rolling back a failed upgrade
Which is on the todo list... I am waiting then :)

I understand why mixing stable and current pkgsrc is a bad idea, but that s how I got my packages working on my fresh NetBSD install when they didnt want to build properly from current...I guess I was lucky to do that without problems :)
I thought that building from stable, then building from current, and installing current if it worked, otherwise stable, would do the trick...

I ll think about another way to do that then...
And about pkg_comp, I guess it looks more like a tool for debugging install process, instead of an "enduser pkgsrc tool", thats why I didnt use it...

Thank you for your help anyway ;),

--
Asmodehn