Degrade, upgrade

[Kovács Péter]

Hello guys,

I have a system running FreeBSD 5.2.1 and want to degrade it
to FreeBSD 4.10 (because the program I want to use only runs
and supported on that platform) without reinstalling the system.
Is it enough to cvsup to the RELENG_4 branch and recompile
the system?
Should I recompile all the programs that were previously
compiled in the FreeBSD 5 environment?

I would also like to know how this works backwards (which is
the common way), so to upgrade from 4 to branch 5. Is there
some kind of tutorial for this?

Thanks,
P.