Pretend & append custom field

[Tester Testson]

Hi,

I have a local Jira Software v6.3.5.1 and have been asked to generate a clickable link in the browser (only IE works) from a "local" link. Another software generates a URN adress to the local destination and I'd like to add the following text before and after to get it working.

Text that needs to be added

Prepended : [http://pw.ol.gs/?

 Appnd: ]

So if I in the custom field "Local link" input "URN=123" and click create I'd like the created issue to display "[http://pw.ol.gs/?URN=123]" in the Local link field. 

My initial thought was to do it through the Update Issue Custom Field option in postscript of the transiton but I'm no coder and have thus been searching the forums for a solution without luck, if anyone could assist it'd be greatly appreciated! 

Unfortunately I don't have access to scriptrunner  or other nifty utilities :/