Applying security patches to old previous quarter ports

[np1]

Hi,
I need to keep packages from previous quarter and update them when security issues are found.
My idea is to `svn` the ports tree and build everything I need using `synth`.
Which is the best way to bring security patches or updated ports in?
I tried to checkout a single port directory but it doesn't seem to work.
Is there a way to checkout only the MFH commits and apply them to the old ports tree?

Thanks