Held You can make a condition that checks what animation/frame the object is on, so for example: On collision with "Enemy1", if playing animation "Circle" Destroy "Enemy1". That way your game will know what to do if it is playing a different animation.
But there is nothing wrong with using different sprites either, its just a little harder to manage and means you have more code. You could also use Arrays for this but if your new to construct 2 I wouldn't get into them just yet ^_^!
In connection with your collision mesh, if you double click a sprite there is an icon at the bottom of the Left hand side panel in the edit image box that is called set collision polygons, you can set this to be different for each animation or frame ( you can al,so right click to apply the same collision mesh to the entire animation or even ALL animations )