Build packages for an older NetBSD version in chroot - can OS_VERSION in BUILD_INFO be changed to other kernel version than host?

[Matthias Petermann <mp%petermann-it.de@localhost>]

Hello all,

Today I came up with a question about the following scenario:

I have a host with a bare metal installation of NetBSD 9.99.96. On this 
host I have two sandboxes (chroots) - one with the same userland as the 
host (9.99.96) and one with the userland of NetBSD 9.2_STABLE.

In the sandboxes I build pkgsrc packages with pbulk, each separately for 
both NetBSD versions. My assumption here is that the 9.99.96 kernel is 
backward compatible as far as it goes.

Is there a standard way to achieve that packages built in 9.2_STABLE 
userland reflect this in the OS_VERSION (+BUILD_INFO in the .tgz) in 
this constellation? I understand that this parameter is apparently 
derived from the kernel version of the host at build time. This is here 
9.99.96. However, in the case described, this seems to cause a warning 
to be issued when installing these packages on a 9.2_STABLE client 
system that the packages were built for a different version.

I would appreciate an answer (and perhaps a solution).

Many greetings
Matthias