AddOns can't change game behavior, they are purely cosmetic.
As for the dungeon exit timer, i agree, this is a pain.
Players have proposed solutions for a long time but ZOS has been silent on the problem.
I think a "story mode" option is long overdue.
The only way i know of to not get kicked at the end is to solo the dungeon.
When you are not in a group, there is no exit timer and you can stay in the dungeon as long as you want.
This issue is a pain. I was running an alt through a dungeon the other day, and at the end I asked to be passed the crown so I could run back to finish the quest and get the skill point and the crown said 'no' and immediately disbanded the group. What an a-hole.