Me. How is the vial held in place, plaster or glue?
If plaster soak in water and then gently pick away at the plaster till the vial is free.
When replacing, make a square of paper the same size as you took out and fold it in reducing concertina fashion.
Slide the paper and vial back in place and then use plaster to reseal.
One proviso, the vial tube usually has a dimple sticking out where it was sealed, keep that clear of plaster.