No direct way to modify god powers other than their attack and in some cases duration. However you can indirectly modify what they do by using triggers to hook onto them either by detecting when they are cast or by detecting the units they create.
Removing the stun effect is a non trivial thing - couple of avenues you could go down but both are very advanced are:
(1)kb query for units that are stunned and change them to themself
(2)y trigger to detect shockwave stun effect to change unit to itself
Both the above would require custom triggers/scripting so maybe the alternative below easier but slightly different to what you asked:
(1)Use lure god power with change units in area to a geyser object, heka gigantes, or some other knocking unit with limited lifespan.
(2)Modify SPCMeteor or Meteor to deal no damage with modify protounit so it only knocks.
[This message has been edited by nottud (edited 07-25-2020 @ 02:39 PM).]