We have a UR20 running a pick and place program, the operator needs to be able to reactivate the grippers which are connected via RS485 and sometimes lose connection. However we have an occasional issue where someone selects the program tab and adds a line in the program which then halts the operation. Is there a way to lock the program editing without preventing access to the installation? I have seen some similar posts but no answer which resolves the problem.
There’s no built-in feature that allows this. Maybe some URCap that allows this exists, but I don’t know of any, either.
You could go the way of making your own URCap, but that might take too much work if you’re not familiar with the environment. 
Can you reactivate via a script command?
If so, you can put a push button by the TP and then run a thread that when the PB is pressed it reconnects the RS485.
I do something similar to this to reset variables that are used in the background.
There is no way to lock out the programming window and prevent inadvertent command entry. Maybe you could create a thread that monitors communication to the gripper and when it fails generate a popup that tells the operator this and then gives them the option to manually clear the fault (like a pushbutton but on the TP).