Possible to add to running Raspbian

I have a PI2 running utilities and a fair amount of setup. Is it possible to add RASPLEX rather than reinstall?

No.

Regards

You could duel boot it via n00bs or berryboot. But as @NedtheNerd has had to point out many times on the forum, Rasplex cannot be installed on top of another OS. It is a fork of an OS and an OS can cannot be installed on top of another OS.