After noticing Kira Meru's facial scar, Gul Dukat requests a dermal regenerator to heal it. Dermal regenerators close open wounds by encouraging growth of the surrounding flesh and knitting it back together at a cellular level. Meru's wound has already healed and developed scar tissue. That tissue would need to be removed before any healthy skin could be generated there. Simply waving a dermal regenerator at a scar would have no effect.
When Kira is sent back in time, she arrives with a new set of clothes and different hairstyle but the same large earring on her right ear. In Bajoran culture, that earring is very personal and denotes identity and family history. Seeing her with it would give away her identity to the family members she sees in the past, or at least raise their curiosity about how she has a symbol of their family.
If Major Kira actually traveled back in time, she would have made drastic changes to the timeline, living in the past for several weeks and altering the lives of numerous people in incalculable ways. Her recklessness in the past is never addressed.
Major Kira is given a bomb disguised as an earring to sneak into Dukat's quarters. It is much larger and of a different design than the one she'd been wearing. In Bajoran culture, that earring is very personal and denotes identity and family history. The Cardassians Kira has interacted with might not notice the change in her earring, but the Bajoran collaborators would.
The resistance fighter tells Major Kira that the bomb has a blast radius of 20 meters. When it goes off, its impact only kills a pair of Cardassian soldiers who were in the doorway to Dukat's quarters where the bomb was set. If the bomb truly had a blast radius of 20 meters, it should have killed everyone in that hallway. If the blast wasn't strong enough to travel through walls, then Dukat being in his study when it went off would have spared his life, and the bomb was effectively worthless.
Major Kira goes to great lengths to not let the drunk legut into her quarters but ignores the most obvious excuse: she shares quarters with Kira Meru and Dukat ordered that Meru's privacy was to be respected (Nerys is unaware that Meru had just been moved to Dukat's quarters).