There are three major properties of the liquids:
- Fat based (oil, melted butter, bacon drippings, and on) versus water based (milk, juice, water, and so on).
- Flavor - some liquids, juices and to a lesser extent, milk have a distinct flavor that will effect the bread
- Acid - Some liquids, like orange juice, are more acid and affect the pH of the dough
Not every liquid falls neatly into these exact categories. Milk, for example, is about 87% water, 4% fat, and the rest is sugars and proteins. These differences are often insignificant compared to the overall bread recipe.
In general, you can substitute fat-based liquids for other fat based ingredients, and water based liquids for other water based liquids.
Most breads also have the capacity to carry additional fats and sugars (called enrichment), which at its extreme leads to breads like brioche which are very sweet and fatty.
Eggs are a complex ingredient in that the whites are mostly water, with some protein (albumin), and the yolks are about 50% water and 50% fat.
Are there any general principles of ingredient substitutions? Note that in a bread recipe, with so few ingredients and a deceptively complex chemistry, all of the ingredients have a role to play in the chemistry, so the major factors you are looking at are the overall total ratios of fat, sugar, and water to the flour. Accent ingredients would be add ins like carway seeds in rye bread which don't incorporate into the dough.
In regards to your desire for more olive oil flavor, you almost certainly can substitute olive oil for any fats already in the recipe with comparable results. Most dought can even carry a little more fat, although this will inhibit yeast growth and gluten development, so that you will need more kneading and more proofing time.
You can also brush the crust with olive oil before or after baking.
The very best way to get olive oil flavor into your bread is to dip it in oil when you eat it. This also allows you to get the full flavor of a quality oil, as many nuances would be lost if it was baked into the bread.