Pipeline to highlight only changed fields

You can use the $prev syntax within a field reference in Pipelines as a way to look at the prior value. You may have to get creative with your email but you can highlight the value of a field and its prior value using {{a.field}} and {{a.$prev.field}}. 

What that means for your email is a little trickier - you could do something super generic like: 

Field Value: Current: {{a.field}} / Prior: {{a.$prev.field}}

If you want a more styled email you'll probably have to get creative with doing {% if %} conditions to check if the value is different and then try and change the email accordingly.