As far as I know the only way is to import the change as a new policy.
On my Space boxes, I import into a new policy and open the new policy, right click on the imported policy rule, copy the rule into clipboard, then go to the orginal policy and paste the rule in. Then delete the newly imported policy ie the one i did the copy from.
It is a pain, but its the only way i have found that works.
After speaking to my Juniper SE, it looks like they are not going to fix this issue any time soon.
Rgds
John