The location of junos.xsl is changing in 12.3, but that should be transparent to scripts due to the import symlink, so ../import/junos.xsl" will continue to work fine.
One problem that can happen, though, is that if you run 12.3 on a box and then downgrade you'll lose a working import symlink and will need to recreate it:
cd /var/db/scripts
rm import
ln -sf /usr/libdata/cscript/import import
Any chance that you had 12.3 on this box before? Perhaps the beta code?
I'd advise against using an absolute import path. Especially since you know it'll break in 12.3.