First of all, I am not admitted in the great state of Texas. However, I would make an attempt to answer this based on general principles of law. Once you gave someone easement like the utility company, they can ask for something more (enlargement) which are reasonable, equitable and consistent with their original easement. Here, it is only 5 feet more. Again, they may place sign to anyone not to do anything close to this easement, so you are not going to use this additional land anyway. As usual, it is best to see a local attorney in your jurisdiction.
Only see a licensed attorney before you make any decision. This answer may not be perfect in any given situation. However, more fact may be required by your local attorney