When you import the word doc into Designer you are given two options. One is to maintain the fidelity of the word doc (basically an image is created and you can lay fields on top of it) or we can attempt to change word objects into xfa objects. In this case some best guesses must be made and you may not get as good a looking document. In the 1st case there are no objects to adjust so to answer your question no you cannot adjust the double lines. In the 2nd case, because objcts are created you will be able to adjust the lines or remove them completely and put a new one in.