Switching user and environment variables to root to install packages

["Rocky Hotas" <rockyhotas%post.com@localhost>]

Hi everybody!
In order to install new pagkages with pkgsrc it is necessary to set the 
environment variables PATH and PKG_PATH.
This can be done for root, which have the needed permissions to install new 
packages.
With a common user and the command su it can be still possible to have the 
necessary permissions, but the variable PATH and PKG_PATH are not set.
So, I would like to ask two question:
- which is in such cases the best approach? To set PATH and PKG_PATH in 
/etc/profile for all users or to mantain the actual configuration?
- Is there a way to completely switch the user and its environment variables?
Thanks!

Rocky