Now that I am in front of my computer, here is the syntax you need:
tmsh modify ltm virtual my-vs profiles delete { old-clientssl } profiles add { new-clientssl }
Here is a bash one-liner which will replace profiles "old-clientssl" with "new-clientssl" in all virtuals in /Common:
tmsh list ltm virtual one-line|grep old-clientssl|cut -d' ' -f3| xargs -I_ -n1 tmsh modify ltm virtual _ profiles delete { old-clientssl } profiles add { new-clientssl }
Run this at your own risk. I suggest you change the last "tmsh" to "echo" to test it first.