MORE ABOUT BARRIER'S DECAY RATE
This was originally a mod request on the DAITools freeforums to make barriers not decay at all. A request was put in to make it compatible with my enhanced rejuvenating barrier mod, since they modify the same file. So here's the result. Thanks Wendera for implementing the original version of the no-decay barrier mod, and giving me permission to assimilate it into my mod.

• Vanilla decay rate is 9% decrease per second.
• If set to 0, barrier will not decay at all. 
• If set to a negative value, it will cause your barrier to regenerate instead. Do not confuse barrier regen with mana/health regen.
• Knight Protector skill either decreases decay rate by 35%, or increases barrier regen rate by 35%.  
• This is independent of the party member workaround for rejuv barrier, ie., whether you have the workaround enabled or not, the modified decay rate will work for every party member.
  

WARNING: a regenerating barrier is gamebreaking - you cannot die.

REJUVENATING BARRIER ALL PARTY MEMBERS WORKAROUND EXPLAINED
Patch 11 - The bug causing Rejuvenating Barrier to not work on party members has been fixed. As long as the caster has Rejuvenating Barrier, any barrier that he casts will have the regen effect. The workaround is left in the mod for legacy/cheating purposes.

Patch 7 - In the vanilla game, when a character is shielded by a barrier - any barrier - the game runs a series of checks to see what additional effects will apply. Checking that the caster has Rejuvenating Barrier is one of the checks. However even though in the code it is written caster, in game it checks the target for the passive instead for some unholy reason. As a result Rejuvenating Barrier only works on a character with the passive ability. To get Rejuvenating Barrier to work on other party members who don't have the passive, this workaround removes this check. By doing so, any barrier will automatically grant Rejuvenating Barrier's effects, as though the check is automatically passed.

Implications: 

• ANY barrier casted by ANY party member will have the regeneration bonus, which is closer to what the tooltip says
• You don't need to spend points to get the passive ability to have its regeneration bonus while under barrier
• You still need to spend a point to get the passive to get the +3 constitution bonus
• Enemies do not benefit from this workaround (tested only on wraiths and rebel mages)
  

You can therefore make barrier a gradual health regenerating barrier with the following configuration options:

• Type of Regeneration: Health
• Regeneration Rate: 3 (heals 3% max health per sec, feels the most balanced to me)
• Workaround: regen for everybody? - Enable
  

For example, with the workaround, Vivienne has the basic barrier ability only (1 point in the spirit tree only). She does not have the +3 constitution bonus. She casts barrier on Blackwall and herself. Both benefit from the regeneration bonus as long as the barrier is active. 

Without the workaround, ie. vanilla, let's say Vivienne has the left side of the spirit tree, ie. she has spent a point on Rejuvenating Barrier. She has the +3 constitution bonus. She casts barrier on Blackwall and herself. Only Vivienne benefits from the regen bonus as long as the barrier is active.

In another scenario, without the workaround, say Vivienne only has the basic barrier spell (1 point in the spirit tree only). Solas however has spent a point in Rejuvenating Barrier. Vivienne casts barrier on Solas and herself. Only Solas benefits from the regeneration bonus as long as the barrier is active.