If you keep your painting smooth, especially if you are painting several objects such as boats, houses, people and certainly portraits, you will have no trouble making changes later, even years later. No hard edges. By that I mean don't leave a ridge of paint at the edge of a subject. Always start at the edge of your subject and pull the brush inward. This eliminates a hard edge. Remember, the subject usually should emerge from the background rather than be planted on it. Go over the lines. It helps. Be loose but also careful. Don't be afraid to merge the subject's color into its background color.
My previous post is a tip on what happens when you have hard edges and want to rework your painting years later. You have to remove the hard edges first by sanding them smooth.
One of my first instructors, who was an English portrait painter, always told me to keep it smooth. Thick paint has its place but make sure you are in the final stages before making it thick. This applies to both oils and acrylics.
