Yes, simply cvsup your /usr/src directory to update it, and recompile the kernel. cvsup will update your source tree to include all the latest security updates.
For future reference, if you compress your kernel into tbz format, place it in /PCBSD/kernels and update the kern.ini file in there to include your new kernel it won't get trashed when we update your kernels, you'll be able to re-select it from the 'System' tool.
If you're unsure how to do this look at how we've compressed the kernels in /PCBSD/kernels, the kern.ini file should be obvious, but if it isn't I'd be happy to explain it.
PC-BSD Lead Developer
tim at pcbsd.org