Yes you can substitute quail eggs for chicken eggs when you want too or need to in a recipe.
For example if you are baking a cake and need to use eggs but only have quail eggs or want to use quail eggs instead of chicken eggs you can use the quail eggs as a substitute for the chicken eggs.
Quail eggs do taste a bit different than chicken eggs though so you may notice a change in taste with the quail eggs when used in a cake or other recipe.
But I have baked cakes with quail eggs before and it actually tasted pretty good.
You can basically use any edible eggs in a recipe that calls for chicken eggs but just be aware that the eggs can taste different.
Also you can eat quail egg shells and they are healthy for you.
When eating quail egg shells you should grind the quail egg shells up into a powder and then eat them that way otherwise it can be hard to chew the quail egg shells and they could pose a choking hazard when eaten without grinding them up.
The quail egg shells are a great source of calcium as well as other nutrients and minerals that our bodies need to stay healthy.
The quail eggs themselves are also very good to eat and health although quail eggs are more expensive than chicken eggs because there's not as many mass produced quail eggs as there are chicken eggs.
Quail egg shells contain 90% calcium carbonate and contains lots of essential minerals for the body, like copper, zinc and lots more.
Chicken egg shells can also be eaten as well and you'll get calcium and other nutrients and minerals from those as well.