Any method to cross build and install to local box

[Paul.LKW]

Hello all:
As I known FreeBSD has a function called cross-build, which can be
build from architecture i386 to Architecture amd64  or wise versa. But
I have freebsd 4.11 (it must be i386 arch.) installed on a AMD-64
mechine and upgraded to 5.4 and want upgrade to 6.0 stable then. Can I
completely change the OS's arch. via the upgrade process (Not Clean
Install) via the following make:

make buildworld TARGET_ARCH=AMD64
make buildkernel TARGET_ARCH=AMD64
make installkernel TARGET_ARCH=AMD64
mergemaster -p
<reboot to single user mode>
make installworld TARGET_ARCH=AMD64