Only works for vanilla guards but..

If you want the feature to work on custom made guards(guards added by other mods), 

USING PATCHER
1. Copy the contents of the patcher folder to your Morrowind data files folder, you must also have tes3cmd in it.
2. Open PGFOMW.pl file using a text edtior e.g Notepad++.
3. Replace/insert the name of the mod you'll want to patch
4. For example, If you use Yet Another Guard Diversity by Half11, then it should look like Picture 1.
5. Save the pl file and then run PGFOMW-Patcher.bat.
6. Wait a few 'moment' for the patching to complete. Usually completed in a blink. Version 1.2.
7. A new esp file called PGFOMW-Patched.esp will be created in your data files folder.
8. Put it at the bottom of your load order and activate it.
9. To play, make sure the listed mods in step 3 and protective guards mod are activated too.
10. The patcher will only patch NPCs with class 'guard' and without any scripts attached to them.

MANUAL PATCHING
Simply assign the the script from this mod to the custom guards in the CS. The script you need to attach is called "EQNX_HELP_PC" without quotes.
1. Open OpenMW-CS, Choose Create Addon instead of Edit Content, select Morrowind, and the plugin you want to patch. 
2. Go to objects window
3. Filter the list to show NPCs with guard class 
4. Just copy paste the script name to the NPCs script data field.
5. Look at manual patching picture..
6. The advantage of this is greater control over which NPC to apply the script and easier to understand, unless you don't mind programming in perl.

If you find any peculiarities during your gameplay, inform me in the modpage.

Obviously, this is not a final work. OpenMW is developing, and this mod will follow up with development.