I have seen this implemented well in other games (Royal Revolt II):
essentially, have an option for Clan members to attack their own clan mates. No loot will actually be gained, nor spells/troops expended... just a free fight that generates a replay that can be shared. The clan castles/troop numbers/traps/etc would be reset to the state there were at when starting. Attacking in this way should neither break an active shield nor generate a shield from defense.
To make it easy, the actual troops deployed would be whatever the offense had in their camps/castle/spell base.
The positive benefits would be:
1. lots of fun for the players, more clan comradery
2. Ability to show clan members how defense could be improved
3. An opportunity to test units before using (squandering?) them
I cannot think of any way this could be abused, as it wouldn't generate loot, shields, or use up any troops/traps.
